Heat-bondable composite fiber, process for producing the same, and fibrous mass

ABSTRACT

A POM/POM thermoadhesive conjugate fiber is produced by providing two kinds of POM-based polymers A and B which satisfy 30&lt;MI A  wherein MI A  is a before-spinning melt index (g/10 min) of the POM-based polymer A (conditions: 190° C., load: 21.18N (2.16 kg)), and T B &gt;T A +10 wherein T A  and T B  are before-spinning fusion peak temperatures of the POM-based polymers A and B respectively, compositely spinning a first component containing the POM-based polymer A and a second component containing the POM-based polymer B such that the first component is exposed with an exposed length of not less than 20% relative to a peripheral length of the fiber, subjecting the spun fiber to a drawing treatment, and subjecting the drawn fiber to an annealing treatment at a temperature of from 60° C. to 110° C.

TECHNICAL FIELD

The present invention is related to a thermoadhesive conjugate fiberwherein a core component and a sheath component are formed frompolyoxymethylene-based polymers and the sheath component hasthermoadhesiveness and the production method of the fiber, and a fiberassembly including the fiber.

BACKGROUND ART

Polyoxymethylene is called “polyacetal” and known as an engineeringplastic which is excellent in electrical insulation, heat resistance andchemical resistance. The molded article of the polyoxymethylene iswidely used as, for example, a component of a car. Since thepolyoxymethylene has excellent crystallizability and present a highcrystallization speed and a large crystallinity, it is said that it isdifficult to produce a fiber from this resin. Nevertheless, theproduction of the fiber from the polyoxymethylene has been tried by i)selecting a particular polyoxymethylene resin, ii) mixing a particularadditive with the polyoxymethylene, or iii) compositely spinning thepolyoxymethylene combined with a particular polymer, in order that theexcellent properties of the polyoxymethylene is utilized (PatentLiteratures 1 to 5). Further, a multi-layer oxymethylene-based copolymerfiber has been proposed, wherein a cross-section structure has at leasttwo layers, every layer is exposed to a surface of the fiber and anamount of comonomer in a copolymer that forms each layer is defined.

[Patent Literature 1] Unexamined Japanese Patent (Kokai) Publication No.H1-272821

[Patent Literature 2] Unexamined Japanese Patent (Kokai) Publication No.H8-144128

[Patent Literature 3] Unexamined Japanese Patent (Kokai) Publication No.H11-293523

[Patent Literature 4] Unexamined Japanese Patent (Kokai) Publication No.2003-268627

[Patent Literature 5] Unexamined Japanese Patent (Kokai) Publication No.2006-9205

[Patent Literature 6] Unexamined Japanese Patent (Kokai) Publication No.2008-138331

DISCLOSURE OF INVENTION Problems to be Solved by Invention

In the case where the polyoxymethylene is made into a fiber and aproduct (such as civil engineering and construction material, aninterfacing, a cushion, and a mat) is manufactured of a nonwoven, awoven fabric, or a knitted fabric which is formed of the fibers, and acomponent other than the polyoxymethylene is not included in theproduct, the properties of the polyoxymethylene is utilized maximally.In other words, when the fibers are made into the nonwoven or the likeand another binder component is included in the nonwoven, some bindersmake the chemical resistance of the product poor as a whole, even thoughthe fiber itself is formed from the polyoxymethylene. The same isapplicable to a conjugate fiber which comprises of the polyoxymethyleneand another polymer. The present inventors considered that, in order toavoid such inconvenience, it is only necessary to form the fiber onlyfrom the polyoxymethylene and have the fiber itself function as thebinder. More specifically, when the two polyoxymethylenes which havedifferent melting points are compositely spun with one component being athermoadhesive component, a sheet, particularly a nonwoven, wherein thefibers are integrally bonded can be obtained without using the anotherbinder component.

A sheath-core conjugate fiber wherein two kinds of polyoxymethylenes areused is disclosed in Patent Literature 5. The conjugate fiber describedin Patent Literature is proposed for the purpose of achieving a highknot strength retention and is not intended to be used as thethermoadhesive fiber. Further, the conjugate fiber produced by a methoddescribed in Patent Literature 5 does not necessarily have sufficientproperties as the thermoadhesive fiber. Furthermore, a fine fiber couldnot be obtained when the present inventors produced the conjugate fiberby the method described in Patent Literature 5. The multi-layer fiberdescribed in Patent Literature 6 is intended to have good crimpability.Therefore, if a thermoadhesive nonwoven is produced using this fiber,difference in area of the nonwoven between before and after thermaltreatment is large due to crimp of the fiber, whereby it is difficult toobtain the nonwoven of a predetermined dimension. The present inventionwas made in light of these situations, and an object of the presentinvention is to provide a thermoadhesive conjugate fiber formed mainlyfrom the polyoxymethylene.

Solution to Solve Problems

When the sheath component of the sheath-core conjugate fiber producedonly from the polyoxymethylenes by the method described in PatentLiterature 5 was melted or softened as the thermoadhesive component toproduce a sheet-shaped product, the core component significantly shrankand it was difficult to obtain the sheet-like product. Then, the presentinventors have reviewed various kinds of polyoxymethylenes and thevarious production conditions in order to suppress the shrink of thecore component. As a result, they have found that a fiber whichfunctions well as the thermoadhesive conjugate fiber by usingpolyoxymethylenes which have a particular difference in melting point,one polyoxymethylene having a high melt index as the sheath component;and employing particular drawing conditions and drying conditions.Further, the inventors found that 150° C. ½ crystallization time, and/orMz (Z-average molecular weight) of the core component effectsspinnablity of the conjugate fiber and that it is important to selectthese parameters appropriately, particularly when a fine fiber isproduced.

In a first aspect, the present invention provides a thermoadhesiveconjugate fiber including a first component as a thermoadhesivecomponent which contains a polyoxymethylene-based polymer A and a secondcomponent which contains a polyoxymethylene-based polymer B, wherein thefirst component is exposed with an exposed length of not less than 20%relative to a peripheral length of the fiber,

which fiber satisfies:

30<MI_(A) wherein MI_(A) is a before-spinning melt index (g/10 min) ofthe polyoxymethylene-based polymer A, which is determined according toJIS K 7210 (conditions: 190° C., load: 21.18N (2.16 kg)), and

Tf_(B)>Tf_(A)+10 wherein Tf_(A) and Tf_(B) are after-spinning fusionpeak temperatures of the polyoxymethylene-based polymers A and Brespectively, which are determined according to JIS K 7121.

Selecting two kinds of polyoxymethylene-based polymers so that MI_(A),Tf_(A) and Tf_(B) satisfy the above relationships suppresses the shrinkof the second component when the first component is heated so as tofunction as the thermoadhesive component, which results in good adhesionbetween the fibers.

Further, in a second aspect, the present invention provides athermoadhesive conjugate fiber including a first component as athermoadhesive component which contains a polyoxymethylene-based polymerA and a second component which contains a polyoxymethylene-based polymerB, wherein:

the first component is exposed with an exposed length of not less than20% relative to a peripheral length of the fiber,

a before-spinning 150° C. ½ crystallization time of thepolyoxymethylene-based polymer B is from 10 seconds to 100 seconds, and

Tf_(B)>Tf_(A)+10 wherein Tf_(A) and Tf_(B) are after-spinning fusionpeak temperatures of the polyoxymethylene-based polymers A and Brespectively, which are determined according to JIS K 7121.

The crystallization time relates to a time until the molten resinsolidifies. By limiting the 150° C. ½ crystallization time of thepolyoxymethylene-based polymer for the second component, thecrystallization is accelerated and therefore solidification proceedsduring the discharge of the molten resin from nozzles and the draft ofthe discharged resin at a predetermined draft ratio. This increases thespinnablity and particularly makes it possible to obtain a spun filamenthaving a small fineness.

The second aspect may be combined with the first aspect. Suchcombination provides better spinnability and makes it possible to obtainthe fiber having a smaller fineness.

In any aspect (or another aspect) of the thermoadhesive conjugate fiberof the present invention, the before-spinning Z-average molecular weight(Mz) of the polyoxymethylene-based polymer B is preferably 500,000 orless. Further, it is preferable that, in any aspect, the thermoadhesiveconjugate fiber of the preset invention is one wherein theafter-spinning Z-average molecular weight (Mz) of the polyoxymethylenepolymer B is 350,000 or less.

Mz is a parameter which relates to a high-molecular-weight component ofa polymer. As the value of Mz is larger, the crystallization speed ishigher. In the present invention, the crystallization speed of the corecomponent is adjusted by defining the upper limit of before- and/orafter-spinning Mz of the polyoxymethylene-based polymer B, whereby thespinnability of the entire conjugate fiber is improved.

In any aspect, the thermoadhesive conjugate fiber is preferably asheath-core conjugate fiber consisting of a first component and a secondcomponent wherein the first component is a sheath component and thesecond component is a core component. Since the first component occupiesall the length of the peripheral surface in the sheath-core structure,the fiber having such structure presents more favorable thermaladhesiveness.

In the case where the thermoadhesive conjugate fiber of the presentinvention is the sheath-core conjugate fiber, it may have an eccentricsheath-core cross section wherein a center position of the secondcomponent is shifted from the center position of the fiber. The fiberhaving such cross-sectional structure tends to develop three-dimensionalcrimps and confers stretchability, bulkiness and/or soft feeling to, forexample, a nonwoven made of the fibers.

In a third aspect, the present invention provides a method for producingthe thermoadhesive conjugate fiber of the first aspect of the presentinvention, which includes:

providing two kinds of polyoxymethylene-based polymers A and B whichsatisfy:

-   -   30<MI_(A) wherein MI_(A) is a before-spinning melt index (g/10        min) of the polyoxymethylene-based polymer A, which is        determined according to JIS K 7210 (conditions: 190° C., load:        21.18N (2.16 kg)), and    -   Tf_(B)>Tf_(A)+10 wherein T_(A) and T_(B) are before-spinning        fusion peak temperatures of the polyoxymethylene-based polymers        A and B respectively, which are determined according to JIS K        7121,

compositely spinning a first component containing thepolyoxymethylene-based polymer A and a second component containing thepolyoxymethylene-based polymer B such that the first component isexposed with an exposed length of not less than 20% relative to aperipheral length of the fiber,

subjecting the spun fiber to a drawing treatment, and

subjecting the drawn fiber to an annealing treatment at a temperature offrom 60° C. to 110° C.

This production method is characterized in that the twopolyoxymethylene-based polymers are selected so that MI_(A), T_(A) andT_(B) satisfy the above relationships and the annealing treatment isconducted at a temperature of from 60° C. to 110° C. after spinning thefiber. These characteristics make it possible to obtain thethermoadhesive conjugate fiber which presents good cardability and smallshrink of the second component upon thermal adhesion of the firstcomponent. A more preferable annealing treatment temperature is from 60°C. to 90° C.

In a fourth aspect, the present invention provides a method forproducing the thermoadhesive conjugate fiber of the second aspect of thepresent invention, which comprises:

providing two kinds of polyoxymethylene-based polymers A and B, thepolymer B having a before-spinning 150° C. ½ crystallization time offrom 10 seconds to 100 seconds, and the polymers satisfyingTf_(B)>Tf_(A)+10 wherein T_(A) and T_(B) are before-spinning fusion peaktemperatures of the polyoxymethylene-based polymers A and B respectivelywhich temperatures are determined according to JIS K 7121,

compositely spinning a first component containing thepolyoxymethylene-based polymer A and a second component containing thepolyoxymethylene-based polymer B such that the first component isexposed with an exposed length of not less than 20% relative to aperipheral length of the fiber,

subjecting the spun fiber to a drawing treatment, and

subjecting the drawn fiber to an annealing treatment at a temperature offrom 60° C. to 110° C.

This production method is characterized in that the two kinds of thepolyoxymethylene-based polymers are selected so that the before-spinning150° C. ½ crystallization time of the polyoxymethylene-based polymer Bsatisfies the above relationship and T_(A) and T_(B) satisfy the aboverelationship and that the annealing treatment is conducted at atemperature of from 60° C. to 110° C. after spinning the fiber. Thesecharacteristics make it possible to obtain the thermoadhesive conjugatefiber which presents good cardability and has a small fineness. A morepreferable annealing temperature is from 60° C. to 90° C.

The fourth aspect may be combined with the third aspect. Suchcombination makes it possible to produce the thermoadhesive conjugatefiber which passes the carding machine well, has a small fineness andpresents a small thermal shrink upon the thermal adhesion.

In the production method in any aspect of the present invention, thespinning is preferably conducted with a draft ratio of from 100 times to1000 times and the drawing treatment is preferably conducted with a drawratio of from 4 times to 10 times. Setting the draft ratio and the drawratio within these ranges gives the thermoadhesive conjugate fiber whichhas more favorable cardability and presents less shrink of the secondcomponent upon the thermal adhesion. Further, setting the draft ratioand the draw ratio within these ranges enables the fineness to be small,for example, from about 0.1 dtex to about 3 dtex.

In a fifth aspect, the present invention provides a fiber assembly whichcontains the thermoadhesive conjugate fiber of the first or the secondaspect of the present invention in an amount of 10 mass % or more. Thisfiber assembly may be, for example, a nonwoven or a molded article.

EFFECT OF INVENTION

The thermoadhesive conjugate fiber of the present invention is onewherein both of the low-melting-point thermoadhesive component and thehigh-melting-point component are formed of the polyoxymethylene-basedpolymers. Therefore, when a sheet article such as a nonwoven is madeusing this fiber, the fibers are integrated with thepolyoxymethylene-based component having the low melting point andanother binder component is not required. Such a sheet article presentsthe heat resistance and the chemical resistance of thepolyoxymethylene-based polymer, particularly when it is formed only fromthe thermoadhesive conjugate fibers of the present invention. Further,the fiber assembly containing the thermoadhesive conjugate fibers of thepresent invention has a high water retentivity, slippability, creaseresistance, and bulk recoverability, and/or good wiping-ability.Therefore, the fiber assembly is suitable for applications which requiresuch properties.

EMBODIMENT OF THE INVENTION

The thermoadhesive conjugate fiber includes at least two components eachof which contains the polyoxymethylene-based polymer. In the presentspecification, the polyoxymethylene-based polymer is a polymer whereinan oxymethylene unit is a main repeating unit. Thepolyoxymethylene-based polymer may be a so-called “POM homo-polymer”which is obtained by a polymerization reaction wherein a main rawmaterial is formaldehyde or trioxane, or may be a so-called “POMcopolymer” which is composed mainly of the oxymethylene unit andcontains an oxyalkylene unit which has from two to eight adjacent carbonatoms, preferably CH₂CH₂O, and may have a substituent. The oxyalkyleneunit is preferably contained in the POM copolymer in an amount of 10mass % or less, and more preferably in an amount of from 0.5 mass % to 8mass % as an ethyleneoxide equivalent. The substituent which can bebonded to the oxyalkylene group is, for example, an alkyl group, aphenyl group, or another organic group. Further, thepolyoxymethylene-based polymer may be a copolymer which has anotherconstituent unit, that is, a block copolymer, a terpolymer, or across-linked polymer.

The thermoadhesive conjugate fiber of the first aspect of the presentinvention includes the first component containing thepolyoxymethylene-based polymer A and the second component containing thepolyoxymethylene-based polymer B. The polyoxymethylene-based polymers Aand B satisfy:

30<MI_(A) wherein MI_(A) is a before-spinning melt index (g/10 min) ofthe polyoxymethylene-based polymer A, which is determined according toJIS K 7210 (conditions: 190° C., load: 21.18N (2.16 kg)), and

Tf_(B)>Tf_(A)+10 wherein Tf_(A) and Tf_(B) are after-spinning fusionpeak temperatures of the polyoxymethylene-based polymers A and Brespectively which are determined according to JIS K 7121.

In order that, MI_(A), Tf_(A) and Tf_(B) satisfy the above formulae, thepolyoxymethylene-based polymers A and B are different from each other inat least one of a molecular weight, the kind or the content of thecomonomer which co-polymerizes with the oxymethylene unit.

Specifically, the polyoxymethylene-based polymer A is, for example, apolymer of which MI_(A) is preferably from 40 to 75, and more preferablyfrom 50 to 70, and of which before-spinning melting point T_(A) ispreferably from 140° C. to 160° C. and more preferably from 150° C. to158° C. Such a polyoxymethylene-based polymer is, for example, one whichcontains CH₂CH₂O in an amount of from 3 mass % to 10 mass % as theethyleneoxide equivalent, preferably 5 mass % to 9 mass %. Thepolyoxymethylene-based polymer B is a polymer of which before-spinningmelting point MI_(B) (g/10 min) is preferably from 20 to 80 and morepreferably from 50 to 70, and of which before-spinning fusion peaktemperature T_(B) is preferably from 160° C. to 174° C. and morepreferably from 165° C. to 172° C. Such a polyoxymethylene-based polymeris, for example, one which contains CH₂CH₂O in an amount of from 0.5mass % to 3 mass % as the ethyleneoxide equivalent, preferably from 0.5mass % to 1.5 mass %.

“30<MI_(A)” wherein MI_(A) is the before-spinning melt index MI (g/10min) of the polyoxymethylene-based polymer A means that a resin of asheath component has high fluidity. Therefore, when the thermoadhesiveconjugate fibers of the present invention are processed into a nonwovenand heated to be thermally adhered, there is a tendency that the firstcomponent spreads over a wide area, the adhesive strength becomes highand the strength of the nonwoven is increased. Further, when thefineness is made small, a take-over speed is higher during spinning(that is, a drafting ratio is larger). Therefore, when the resin of thesheath component satisfies 30<MI_(A), the resin has high fluidity, whichgives advantage that the resin is easy to melt and deform duringspinning.

Further, the draft ratio during spinning and the draw ratio during adrawing treatment can be made high to give a finer fiber, by settingMI_(B) (g/10 min) within a range of from 20 to 80 wherein MI_(B) is thebefore-spinning melt index of the polyoxymethylene-based polymer B. As aresult, crystal orientation of the fiber is facilitated, and thereby theshrink of the fiber is expected to be suppressed, whereby a non-wovenshrinkability can be suppressed upon processing the fibers into thenon-woven.

Further, there is a 150° C. ½ crystallization time as the property fordefining the polyoxymethylene-based polymer B. In the conjugate fiber ofthe present invention, the polyoxymethylene-based polymer B preferablyhas the 150° C. ½ crystallization time of from 10 seconds to 100seconds, which time is determined as follow.

[A method for determining 150° C. ½ crystallization time]

A sample of 10 mg is put into an aluminum container and a temperature israised from 20° C. to 200° C. at a temperature rising speed of 10°C./min and the temperature is retained for 2 minutes, using adifferential scanning calorimeter under a nitrogen atmosphere. Then thetemperature is lowered at a temperature falling speed of 50° C./min andis retained at 150° C. The time period between the time at which theretention of the temperature starts and the time at which acrystallization heat-release peak (a peak which appears near 150° C.) isdetermined as the 150° C. ½ crystallization time.

The details of the conditions for determination are as follow:

Differential scanning calorimeter: trade name “DSC 6200” manufactured bySEIKO Instruments;

Atmosphere: nitrogen flow (50 mL/min)

Temperature calibration: pure water, and melting points of high-purityindium and high-purity tin;

Sensitivity calibration: high-purity indium (ΔHm=6.86 cal/g).

Temperature range: 20° C. to 220° C.

When the before-spinning 150° C. ½ crystallization time of thepolyoxymethylene-based polymer B is within the above range, thecrystallization is facilitated and thereby the solidification proceedsto some extent during the discharge of the molten resin and the draftingof the discharged resin at a predetermined drafting ratio. This improvesthe spinnability of the conjugate fiber and particularly enables thespun filament of a small fineness. Particularly when the conjugate fiberis a sheath-core conjugate fiber which is described below, the sheathcomponent tends to be solidified by being cooled by a chimney, while thecore component may not be cooled sufficiently, which makes thesolidification of the component difficult. This tendency is a reason whyit is preferable that the 150° C. ½ crystallization time of thepolyoxymethylene-based polymer B is within the above ramge.

In the case where the 150° C. ½ crystallization time of thepolyoxymethylene-based polymer B is shorter than 10 seconds, the secondcomponent is solidified quickly, whereby the drafting is not made duringspinning; fiber breakage occurs just under the nozzle; and many blockstend to generate. In the case where the 150° C. ½ crystallization timeof the polyoxymethylene-based polymer B is longer than 100 seconds, thecooling during spinning is not sufficient, which causes the breakageduring drafting due to the shortage of a melt tension.

In the case where the 150° C. ½ crystallization time of thepolyoxymethylene-based polymer B is within the above range, it ispreferable that difference between the before-spinning melt indexes MI(g/10 min) of the polyoxymethylene-based polymers B and A is small.Specifically, the ratio (before-spinning MI_(B)/before-spinning MI_(A))is preferably from 0.8 to 1.2. This is because the drafting smoothlyproceeds when the fluidity of the two components are more similar toeach other during the spinning drafting.

In the case where the conjugate fiber having the fineness of about 1.7dtex or less is produced, the before-spinning 150° C. ½ crystallizationtime of the polyoxymethylene-based polymer B is preferably from 15seconds to 50 seconds, more preferably from 20 seconds to 50 seconds,and still more preferably from not less than 20 seconds to less than 30seconds.

Alternatively, the 150° C. ½ crystallization time of thepolyoxymethylene-based polymer B may be determined after spinning. Inthis case, the preferable range of the 150° C. ½ crystallization time isfrom 10 seconds to 100 seconds. The after-spinning 150° C. ½crystallization time of the polyoxymethylene-based polymer B isdetermined, by raising and retaining the temperature according to thedetermination method described above using the conjugate fiber as thesample. In the conjugate fiber having the fineness of about 1.7 dtex orless, the after-spinning 150° C. ½ crystallization time of thepolyoxymethylene-based polymer B is preferably from 15 seconds to 50seconds, and more preferably from 20 seconds to 50 seconds. Thepolyoxymethylene-based polymer A is in a melted or softened state duringthe determination of the 150° C. ½ crystallization time of thepolyoxymethylene-based polymer B in the conjugate fiber, and does notaffect the determination as to the polyoxymethylene-based polymer B.

The polyoxymethylene-based polymer B which has the before-spinning orthe after-spinning 150° C. ½ crystallization time is not necessarilyrequired to be used in combination with the polyoxymethylene-basedpolymer A having the before-spinning MI_(A) within the above range. Inother words, even if the before-spinning melt properties of thepolyoxymethylene-based polymer A is not limited to particular ones, thethermoadhesive conjugate fiber which is spun well and presents goodthermal adhesiveness can be obtained, as long as the before-spinning orthe after-spinning 150° C. ½ crystallization time of thepolyoxymethylene-based polymer B is within the above range.

Further, the physical properties which define the polyoxymethylene-basedpolymer B include a Z-average molecular weight (Mz). In the conjugatefiber of the present invention, a before-spinning Mz of thepolyoxymethylene-based polymer B is preferably 500,000 or less which isdetermined under the following conditions.

<Conditions for Determination of Mz>

-   -   Method: GPC (Gel Permeation Chromatography) Conditions:        -   Device: Gel permeation chromatograph GPC (produced by            Waters)        -   Detector: differential refractive index detector RI (Type            2414, sensitivity 256, produced by Waters)        -   Column: Shodex-HFIP-806M two columns (S/N A406246, A406247)            (produced by Showa Denko K.K., φ8.0 mm×30 cm, number of            theoretical plates of about 14,000 plates/two columns)        -   Solvent: Hexafluoroisopropanol (HFIP, produced by Central            Glass Co., Ltd., NaTFA 5 mM added)        -   Flow speed: 0.5 mL/min        -   Sample:        -   (Dissolution) Agitating gently at a room temperature,        -   (Solubility) Visual good        -   (Concentration) 0.05 w/v %        -   (Filtration) Membrane filter with a pore diamter of 0.45 μm            (H-13-5, produced by Tosoh Corporation)        -   (Charged amount) 0.200 mL        -   (Standard specimen) polymethylmethacrylate produced by Showa            Denko K.K.) and        -   Dimethylterephthalate (produced by Tokyo chemical industry            Co., Ltd.).        -   Determination of Mz: Mz is determined from the following            formula:

Mz=Σ(Ni·Mi ³)/Σ(Ni·Mi ²)

-   -   -   wherein Mi is a molecular weight at an elution position of a            GPC curve which is obtained through a molecular weight            calibration curve, and Ni is a number of molecule.

The spinning was conducted, by the present inventors, in which variouspolyoxymethylene-based polymers are used as the second component. As aresult, they found that difference in distribution of the molecularweight affects the spinnability, even though the before-spinning MI_(B),is the same. Further, they found that as Mz which is a parameterrelating to the high-molecular-weight component of the polymer islarger, the crystallization speed is higher. Specifically, when the Mzof the polyoxymethylene-based polymer B is 500,000 or lower, goodspinnability is achieved. When the composite fiver having a fineness ofless than 2 dtex, particularly 1.8 dtex or less, more particularly 1.6dtex or less, and still more particularly 1.4 dtex, the Mz of thepolyoxymethylene-based polymer B is preferably 390,000 or less, morepreferably 380,000 or less and still more preferably 360,000 or less.When the Mz of the polyoxymethylene-based polymer B is over 500,000 orless, the crystallization speed is high, resulting in deterioration ofthe spinnability. Further, the polymer of such a high Mz generatesunmelted substance upon melting the polymer in an extruder, which causesbreakage of fiber during spinning.

Otherwise, the Mz of the polyoxymethylene-based polymer B may bedetermined after spinning. In that case, the Mz is preferably 500,000 orless. When the Mz is determined by the above determination methodwherein the sample is the conjugate fiber, the Mz of thepolyoxymethylene-based polymer A and the Mz of thepolyoxymethylene-based polymer B are combined and one Mz is determined.However, it is considered that the most of the determined Mz is occupiedby the polyoxymethylene-based polymer B. In the conjugate fiber having afineness of about 1.7 dtex or less, Mz is preferably 350,000 or less,and more preferably 300,000 or less.

When the first component contains a component(s) other than thepolyoxymethylene-based polymer A, it preferably contains thepolyoxymethylene-based polymer A in an amount of at least 50 mass %.When the content of the polyoxymethylene-based polymer is less than 50mass %, the fiber which presents the properties (for example, chemicalresistance) provided by the polyoxymethylene-based polymer cannot beobtained. It is preferable that the first component essentially consistsof the polyoxymethylene-based polymer A. The term “essentially” is usedconsidering that the content of the polyoxymethylene-based polymer A isnot completely 100 mass % in the case where the first component containsan additive such as a stabilizer or the like. The component other thanthe polyoxymethylene-based polymer A contained in the first component ispreferably, for example, a high-density polyethylene, a low-densitypolyethylene, ethylene-propylene copolymer, or polypropylene.

The above applies to the second component.

After-spinning Tf_(A) is preferably in a range of from 138° C. to 160°C., and more preferably from 148° C. to 156° C.

After-spinning Tf_(B) is higher than Tf_(A) by 10° C. or more,preferably 13° C. or more, and more preferably 15° C. or more. When thedifference between Tf_(A) and Tf_(B) is small, the second componentshrinks during the heat adhesion and the fiber loses its form, whereby anonwoven having a shape cannot be formed upon producing the nonwoven,for example.

The thermoadhesive conjugate fiber of the present invention has across-sectional structure wherein the first component is exposed with anexposed length of not less than 20% relative to a peripheral length ofthe fiber. Such structure is preferably a sheath-core conjugate fiberstructure wherein the first component is the sheath component and thesecond component is the core component. The sheath-core structure givesfavorable thermal adhesiveness since the first component which is thethermoadhesive component exists over the entire fiber surface in thisstructure. The sheath-core conjugate fiber may have an eccentricsheath-core cross section wherein the center position of the secondcomponent (the core component) is shifted from the center position ofthe fiber. A fiber having such cross section tends to developthree-dimensional crimps and provides stretchability, bulkiness and/orsoft feeling to, for example, a nonwoven made of the fibers when thenonwoven is made from this fiber. Further, the thermoadhesive conjugatefiber having the eccentric sheath-core cross section can be obtained asa fiber which develops the three-dimensional crimps by subjecting it toa thermal treatment.

In the sheath-core conjugate fiber, a composite ratio of the firstcomponent to the second component is preferably in a range of 3:7 to 7:3by volume. The more preferable range of the volume ratio is from 4:6 to6:4. When the ratio of the first component is less than three, thethermoadhesiveness may be insufficient. When the ratio of the firstcomponent is over seven, the cardability may be deteriorated. Further,the large ratio of the first component makes the bulk of the nonwovenprone to difficult to obtain (that is, the nonwoven lacks forbulkiness), resulting in deterioration of feeling, when the fibers areprocessed to form the nonwoven.

The thermoadhesive conjugate fiber of the present invention may includethe first component, the second component and possibly a third componentcontaining another polyoxymethylene-based polymer to give a constructionwherein all the components are disposed concentrically, or aconstruction wherein the components are disposed to be parallel to eachother. In the case where the thermoadhesive conjugate fiber includesanother component other than the first component and the secondcomponent, it is preferable that the another component also containsanother polyoxymethylene-based polymer and the anotherpolyoxymethylene-based polymer and the polyoxymethylene-based polymer Asatisfy the same relationship as that between the polyoxymethylene-basedpolymer B and the polyoxymethylene-based polymer A, with respect to theafter-spinning fusion peak temperature.

The thermoadhesive conjugate fiber of the present invention can beobtained as a fine fiber having a fineness of from about 0.1 dtex toabout 3 dtex. Fibers of such a fineness is equivalent to those of apolypropylene fiber and a polyester fiber which are widely used as afiber for producing a nonwoven (including a paper (a wetlaid nonwoven)),and therefore makes it possible to produce a fiber assembly(particularly the nonwoven) by a method which is employed when usingthese widely-used fibers.

The thermoadhesive conjugate fiber presents the reduced shrink of thesecond component upon the thermal adhesion due to the use of theparticular polyoxymethylene-based polymers. This is shown by a singlefiber dry heat shrinkage percentage determined according to JIS L 1015(dry heat shrinkage percentage) at a temperature of 140° C., for a timeof 15 minutes under an initial tension (load) of 0.018 mN/dtex (2 mg/d).The thermoadhesive conjugate fiber of the present invention preferablyshows the single fiber dry heat shrinkage percentage of 15% or less, andmore preferably 12% or less, when the center position of the secondcomponent almost coincide with the center position of the fiber, thatis, when the fiber is the concentric sheath-core conjugate fiber.

Further, the thermoadhesive conjugate fiber of the present inventiontends to have a high knot strength retention. Specifically, thethermoadhesive conjugate fiber of the present invention has a knotstrength retention of 90% or more, and more specifically from 96% to98%, when the center position of the second component coincides with thecenter position of the fiber, that is, when the fiber is the concentricsheath-core conjugate fiber. The reason why the thermoadhesive conjugatefiber of the present invention has the high knot strength retention isnot clear, but one reason may be that a smoothness of the fiber of thepresent invention is high, and the fiber is orientationally crystallizedby drawing, resulting in hardening of the fiber. It is considered thatthe knot strength retention tends to be lowered when the fibers aredamaged because they are rubbed on each other upon knotting the fiber.It is presumed that since the thermoadhesive conjugate fiber has a highsurface smoothness and is hard, the damage due to friction is small,leading to the high knot strength retention.

Another reason is that the thermoadhesive conjugate fiber of the presentinvention can be produced being drawn sufficiently at a high draw ratio,and thereby can be obtained as a fine fiber. Since the fine fiber offrom about 0.1 dtex to about 3 dtex is particularly flexible in general,it is presumed that the knot strength retention of such a fine fiberbecomes high.

It is presumed that the crystallization of each component of thethermoadhesive conjugate fiber of the present invention proceeds toharden the entire fiber, since the fiber is preferably produced by aproduction method which involves drawing the fiber sufficiently at arelatively high draw ratio during spinning and drawing. In the hardfiber, mechanical crimps tend to be kept for a long time after thecrimps are given, whereby the fibers are entangled well. This gives atendency that, for example, uniformity of a web which is obtained bycarding the fibers is excellent.

Next, a method for producing the thermoadhesive conjugate fiber of thepresent invention is described. Firstly, two kinds ofpolyoxymethylene-based polymers A and B are prepared, which satisfy:

-   -   30<MI_(A) wherein MI_(A) is a before-spinning melt index (g/10        min) of the polyoxymethylene-based polymer A, which is        determined according to JIS K 7210 (conditions: 190° C., load:        21.18N (2.16 kg)), and    -   T_(B)>T_(A)+10 wherein T_(A) and T_(B) are before-spinning        fusion peak temperatures of the polyoxymethylene-based polymers        A and B respectively after being spun, which are determined        according to JIS K 7121. Such polyoxymethylene-based polymers A        and B are as described above.

In addition to or as a substitute for MI_(A) of the above range, the150° C. ½ crystallization time of the polyoxymethylene-based polymer Bmay be within a range of from 1 second to 100 seconds. Alternatively, inaddition to MI_(A) of the above range and/or the 150° C. ½crystallization time of the above range, the polyoxymethylene-basedpolymer B may have Mz of 500,000 or less. Such a polyoxymethylene-basedpolymer B is as described above.

Then, the first component containing the polyoxymethylene-based polymerA and the second component containing the polyoxymethylene-based polymerB are compositely spun such that the first component is exposed with anexposed length of not less than 20% relative to a peripheral length ofthe fiber. A spinning temperature is preferably from 180° C. to 200° C.The spun filament having an after-drafting fineness in a range of from 2dtex to 15 dtex is made. In the case where the fiber having a finenessof less than 2.0 dtex is intended to be obtained, an after-draftingfineness is made 8 dtex or less. When the after-drafting fineness of thespun filament is less than 2.0 dtex, the productivity of the fiber islowered due to break of filament. When the after-drafting fineness ofthe spun filament is over 15 dtex, the filament is not drawnsufficiently and a fiber with uniform fineness cannot be obtained due tonecking. When an orifice diameter of a spinning nozzle is from 0.3 mm to1 mm, the draft ratio (drawing ratio) during spinning is, for example,preferably from about 100 times to about 1000 times, more preferablyfrom about 300 times to about 900 times, and still more preferably about400 times to about 800 times in order to obtain the spun filament havingthe fineness in the above range. The relatively high draft ratio duringspinning can give, synergized with a later drawing treatment, thethermoadhesive conjugate fiber of which second component presentssuppressed shrink upon the thermal adhesion. The orifice diameter of thespinning nozzle may be selected arbitrarily in order to achieve theabove draft ratio.

Next, the spun filament is subjected to a drawing treatment to give adrawn filament. The drawing treatment is preferably conducted at atemperature lower than the fusion peak temperature of thepolyoxymethylene-based polymer A. Specifically, the drawing temperatureis preferably set at a temperature of from 130° C. to 150° C. The drawratio is preferably from 4 times to 10 times, and more preferably from4.2 times to 7 times. The drawing method is preferably a dry drawingmethod. Alternatively, the drawing may be conducted by a wet drawingmethod.

A predetermined amount of a fiber treatment agent is applied to theresultant drawn filament and then mechanical crimps are given to thefilament with a crimper (a crimp-giving machine) in the case where thefiber is one for being opened and forming a web with a carding machineor for forming an airlaid web. The number of crimps is preferably in arange of from 12 peaks/25 mm to 19 peaks/25 mm. When the number ofcrimps is less than 12 peaks/25 mm, the cardability of the fiber isdeteriorated since winding on a cylinder and fly tend to occur in thecard. Further, a small number of crimps makes a web strength low, whichindicates a degree of entanglement of fibers, and tends to cause troublein the carding process. When the number of crimps is more than 19peaks/25 mm, unevenness such as nep and cloudy tends to generate due tobad openability of the fibers in the carding process. The number ofcrimps is more preferably in a range of from 14 peaks/25 mm to 16peaks/25 mm. In the case where the conjugate fiber is intended to beobtained as a short-length fiber (particularly, a short fiber for makingpaper) having a fiber length of less than 10 mm, the mechanical crimpsmay not be given to the fiber.

After forming the crimps (or applying the fiber treatment agent withoutforming the crimps), the filament is subjected to an annealing treatmentat a temperature in a range of from 60° C. to 110° C. for a severalseconds to about 30 minutes. When the annealing treatment is conductedafter the fiber treatment agent is applied, the annealing treatment ispreferably conducted at an annealing temperature in a range of from 60°C. to 110° C. for a treatment time of at least 5 minutes in order thatthe fiber treatment agent is dried at the same time. When the annealingtreatment is conducted at a temperature in the above-described range,the crimp shape is stabilized which results in, for example, reducedthinning of the nonwoven, whereby a bulky and bouncy nonwoven isobtained when the nonwoven is produced. Further, the annealing treatmentat such a relatively low temperature can suppress the single fiber dryheat shrinkage percentage of the resultant fiber. The annealingtreatment may be omitted when the short fiber for making paper.

After completing the annealing treatment (after applying the fibertreatment agent in the case of the short fiber for making paper), thefilament is cut so that the fiber length is from 3 mm to 100 mmdepending on use. The thermoadhesive conjugate fiber of the presentinvention may be used as a long fiber, if necessary. The thermoadhesiveconjugate fiber of the present invention can be produced by a meltblownmethod and a spunbond method as long as the particularpolyoxymethylene-based polymers as described above are used for thefirst and the second components.

The present invention also provides a fiber assembly which contains thethermoadhesive conjugate fiber of the present invention as describedabove in an amount of 10 mass % or more. The fiber assembly ispreferably one wherein the fibers are bonded by the first component. Thefiber assemblies include a woven fabric, a knitted fabric and nonwoven.The fiber assembly contains the thermoadhesive conjugate fiber morepreferably in an amount of 50 mass % or more and most preferably 100mass %.

Then, the nonwoven is described as an example of the fiber assembly ofthe present invention, together with the production method of thenonwoven. The nonwoven is produced by making a web containing thethermoadhesive conjugate fiber of the present invention in an amount of10 mass % or more and subjecting the web to a thermal treatment to meltor soften the first component of the fiber so that the fibers arebonded. The nonwoven may be produced using a web which is obtained bymixing the thermoadhesive conjugate fiber of the present invention andanother fiber(s), or a laminate wherein a web of another fiber(s) isstacked on the web of the fiber of the present invention. As the anotherfiber, one or more fibers may be selected from a natural fiber such ascotton, silk, wool, hemp and pulp; a regenerated fiber such as rayon andcupraammonium rayon (Cupra); and a synthetic fiber such as an acrylicfiber, a polyester fiber, a polyamide fiber, a polyolefin fiber and apolyurethane fiber, depending on use and so on of the nonwoven.

The fiber mixed with the fiber of the present invention may be asplittable conjugate fiber consisting of two or more resin components.The splittable conjugate fiber has a fiber cross-sectional structurewherein at least one component is divided into two or more segments andat least a portion of each component is exposed on a surface of thefiber and the exposed portion extends continuously in the longitudinaldirection of the fiber. The preferable polymer combination forconstituting the splittable conjugate fiber is, polyethyleneterephthalate/polyethylene, polyethylene terephthalate/polypropylene,polyethylene terephthalate/ethylene-propylene copolymer,polypropylene/polyethylene, and polyethylene terephthalate/nylon.

The webs used for producing the nonwoven include a carded web such as aparallel web, a semi-random web, a random web, a cross-laid web, andcrisscross-laid web; a wetlaid web; and an airlaid web. Two or morefiber webs of different types may be stacked. Further, the fiber web maybe optionally subjected to a second process such as a hydroentanglingtreatment or a needle-punching treatment before and/or after the thermaltreatment in order to entangle the fibers.

The fiber web is subjected to a thermal treatment with a known thermaltreating means. It is preferable to employ at least one thermal treatingtechnique selected from a hot air-through technique and athermocompression bonding technique as the thermal treating means. Theconditions for the thermal treatment such as a thermal treatmenttemperature and soon are optimally selected depending on the thermaltreating technique employed. When the hot air-through technique isemployed, the thermal treatment temperature may be set at a temperatureat which the first component of the thermoadhesive conjugate fiber ismelted or softened, preferably in a range of from 145° C. to 170° C., amore preferably in a range of from 150° C. to 165° C., and still morepreferably in a range of 155° C. to 165° C. This thermal treatmenttemperature is preferably employed when the fiber assembly of anotherembodiment (for example, the woven fabric or the knitted fabric) isproduced.

A mass per unit area is not limited to a particular one, and may beselected from a range of from 10 g/m² to 5000 g/m² depending on the use.Further, a density of the nonwoven may be selected from a range of from0.01 g/cm³ to 1.0 g/cm³ depending on the use.

The resultant nonwoven has excellent slippability because the smoothnessof the surface of the thermoadhesive conjugate fiber is high. Further,the nonwoven is bulky and has cushioning properties. Furthermore, thisnonwoven presents high water retentivity, high bulk recoverability, andhigh crease resistance. Therefore, this nonwoven is favorably suitablefor applications such as hygiene products (menstrual sanitary productsand paper diaper), paper, a wiper, a wet tissue, a mask, an interfacing,a brassiere pad, a civil engineering and construction material, a buffer(including a cushion), a wrapping material, clothes, a mat and asponge-like nonwoven material. Further, the fiber assembly of anotherembodiment (for example, the woven fabric and the knitted fabric) may beused for the same applications.

Particularly when the nonwoven for the wiper is produced, it ispreferable to combine the thermoadhesive conjugate fiber of the presentinvention with the splittable conjugate fiber. The splittable fibergives ultrafine fibers by dividing the fiber, for example, by means ofthe hydroentangling treatment, resulting in a nonwoven wherein thefibers of the present invention and the ultrafine fibers exist on thesurface. Such a nonwoven has high slippability which is conferred by thefiber of the present invention, and is excellent in wiping-ability.Alternatively, a fiber which is widely used for forming the wiper may beused instead of the splittable conjugate fiber. The conjugate fiber ofthe present invention is preferably contained in an amount of from 20mass % to 70 mass %, and more preferably in an amount of from 30 mass %to 50 mass % regardless of the type of the fiber which is mixed with theconjugate fiber of the present invention.

The thermoadhesive conjugate fiber of the present invention is notnecessarily required to be used for bonding the fibers in the fiberassembly. Particularly when the fiber assembly is used as the nonwovenfor the wiper, the fiber assembly is integrated by the fiberentanglement (for example, the hydroentanglement) without beingsubjected to the thermal treatment, so that a softer and a betterfeeling are obtained.

The fiber assembly of the present invention may be a molded articlewhich is produced by conducting the thermal treatment with the fibers orthe fiber web within a mold. For example, the molded article can besimply formed by making the fiber web containing the thermoadhesiveconjugate fiber of the present invention with a carding machine, andputting the web into the mold followed by the thermal treatment. Thekinds of the carded webs are described as above. The thermal treatmentmay be conducted employing the hot air-through technique. The fiber webmay be put into the mold after being subjected to the hydroentanglingtreatment. The molded article having a large thickness may be producedby laminating the fiber webs using a cross-layer machine and putting thelaminated web into the mold. The laminated web may be optionallysubjected to the needle-punching treatment and/or the hydroentanglingtreatment.

The density of the molded article is selected depending on the use ofthe article, regardless of the method for producing the molded article.Specifically, the density of the molded article is preferably from 0.01g/cm³ to 1.0 g/cm³, more preferably from 0.02 g/cm³ to 0.8 g/cm³, andstill more preferably from 0.04 g/cm³ to 0.6 g/cm³. The mass per unitarea is also selected depending on the use. Specifically, it ispreferably from 10 g/m² to 5000 g/m².

The molding process is conducted at a thermal treatment temperature in arange of from 140° C. to 180° C. for the thermal treatment time in arange of from 5 seconds from 120 minutes depending on the mass per unitarea of the fiber web and the intended density of the resultant moldedarticle. Specifically, the thermal treatment temperature is preferablyat least the melting point of the first component of the thermoadhesiveconjugate fiber of the present invention and at most (the meltingtemperature of the second component −5° C.). More specifically, in thecase where the mass per unit area is 100 g/m² or less, the thermaltreatment is preferably conducted using a conveyer type hot air-throughthermal treating machine and setting the thermal treatment time within arange of from 5 seconds to 20 minutes. In the case where the mass perunit area is over 100 g/m², the thermal treatment is preferablyconducted using a batch type hot air-through thermal treating machineand setting the thermal treatment time within a range of from 1 minuteto 120 minutes.

The molding process is preferably conducted using a mold formed from aair-permeable material such as a metal mesh or a resin mesh sheet sothat the thermal treatment is conducted evenly in a thickness directionof the fiber web when using a hot air-through thermal treating machine.For example, the molding process may be conducted by a method whereinthe mold is made by shaping the air-permeable sheet into a predeterminedshape, and then the fiber web is put into this mold. Alternatively, thefiber web may be mold-processed by a method wherein the fiber web issandwiched with two air-permeable sheets (for example, the metal mesh)and then the sandwiched web is shaped into a desired shape and subjectedto the thermal treatment. The shape of the molded article is not limitedto a particular one, and it may be any of a flat plate shape, a shapewith a curbed surface, a box shape, a convex shape, a hat shape, a glassshape, a cup shape, a columnar shape and a spherical shape.

EXAMPLES

Hereinafter, the present invention is specifically described byexamples. In the following examples, the melting points T_(A) and T_(B)of the polyoxymethylene-based polymers A and B which were used as afirst and a second components respectively in the production of fiber.The after-spinning melting point Tf_(A) of the first component, theafter-spinning melting point Tf_(B) of the second component, the singlefiber strength and rupture elongation, the number of crimps, thepercentage of crimp, the knot strength, the knot strength retention, thesingle fiber dry heat shrinkage percentage, the cardability, the areashrinkage percentage of nonwoven, the thickness and the strength ofnonwoven were determined as described below.

[Determination of T_(A) and T_(B)]

A differential scanning calorimeter (manufactured by Seiko InstrumentsInc.) was employed. A sample amount was 5.0 mg. The sample wasmaintained at 200° C. for 5 minutes, and cooled to 40° C. at atemperature falling speed of 10° C./min and then melted at a temperaturerising speed of 10° C./min so that a curve for heat of fusion wasobtained for each of the first component and the second component. Fromthe curve for heat of fusion, the fusion peak temperatures T_(A) andT_(B) were determined as the melting points, respectively.

[Determination of Tf_(A) and Tf_(B)]

A differential scanning calorimeter (manufactured by Seiko InstrumentsInc.) was employed. A sample amount was 6.0 mg. The temperature of fiberwas risen from a room temperature to 200° C. at a temperature risingspeed of 10° C./min to be melted, and Tf_(A) and Tf_(B) were determinedfrom a resultant curve for heat of fusion.

[Mz and 150° C. ½ crystallization time]

These were determined according to the methods which are described in“Embodiment for Carrying Out Invention.”

[Spinnability]

The spinnablity was estimated according to the following standards:

∘ No fiber breakage occurred during 1-hour spinning;

Δ The filament could be take off even though the fiber breakageoccurred;

x The filament could not be taken off because fiber breakage occurredfrequently.

[Tensile Strength and Rupture Elongation of a Single Fiber]

A load and an elongation when the fiber broke were measured according toJIS L 1015 using an extension tensile tester with a sample gage lengthof 20 mm and they were determined as the single fiber strength and thesingle fiber rupture elongation respectively.

[Knot Strength and Knot Strength Retention]

The knot strength of a single filament was determined according to JIS L1013 and the knot strength retention which was a ratio of the knotstrength to the filament strength (the fiber tensile strength) wascalculated.

[Number of Crimps, and Percentage of Crimp]

They were determined according to JIS L 1015.

[Single Fiber Dry Heat Shrinkage Percentage]

Dry heat shrinkage percentages were determined according to JIS L 1015with a gage length of 100 mm at a treatment temperature of 140° C. for atreatment time of 15 minutes under an initial tension of 0.018 mN/dtex(2 mg/d).

[Cardability]

A parallel carding machine was used. A carded web having a mass per unitarea of about 30 g/m² was discharged at a line speed of 10 m/min anduniformity of the carded web, presence or absence of fly, andtransferability of web (continuousness of web transferring from a rollerto a roller) were observed and cardability was evaluated according tothe following criteria:

∘: Favorable as to all of the uniformity of the carded web, the fly,winding and the transferability of the web;

Δ: Bad as to one of the uniformity of the web, the fly, winding and thetransferability of the web; and

x: Bad as to two or more of the uniformity of the carded web, the fly,winding and the transferability of the web.

[Nonwoven-Area Shrinkage Percentage: Samples 1 to 9 and 11 to 16]

The Nonwoven-area shrinkage percentage was determined by the followingmethod.

(1) A carded web having a mass per unit area shown in Tables 1 to 4using a parallel carding machine and it was cut into a square with asize of 20 cm in the lengthwise direction×20 cm in a crosswisedirection. The size (cm) of the web before a shrinking treatment wasdetermined.

(2) The carded web was subjected to a thermal treatment without beingrestricted in order to be shrunk, at a thermal treatment temperatureshown in Tables 1 to 4 and an air flow rate of 1.5 m/sec (upper flow)using a hot air-through thermal treating machine. The thermal treatmenttime was set at 12 seconds.

(3) The size (cm) of the nonwoven after the treatment was determined.

(4) The area shrinkage percentage was calculated based on a followingformula:

${{Nonwoven}\text{-}{{areashrinkagepercentage}(\%)}} = \frac{\begin{matrix}{\begin{pmatrix}{{{Before}\text{-}{shrinking}\mspace{14mu} {lengthwise}} - {{direction}\mspace{14mu} {size} \times}} \\{{crosswise} - {{direction}\mspace{14mu} {size}}}\end{pmatrix} -} \\\begin{pmatrix}{{{After}\text{-}{shrinking}\mspace{14mu} {lengthwise}} - {{directionsize} \times}} \\{{crosswise} - {{direction}\mspace{14mu} {size}}}\end{pmatrix}\end{matrix}}{\begin{matrix}{{{Before}\text{-}{shrinking}\mspace{14mu} {lengthwise}} - {{direction}\mspace{14mu} {size} \times}} \\{{crosswise} - {{direction}\mspace{14mu} {size}}}\end{matrix}}$

[Nonwoven-Area Shrinkage Percentage: Sample 10]

The Nonwoven-area shrinkage percentage was determined by the followingmethod.

(1) 2 L water was put into a household mixer, and 4.4 g fibers were putinto the mixer followed by the mixing for 1 minute. Then, a wet-laid webof 70 g/m² was obtained using a 25 cm×25 cm hand-made paper device. Thesize of the web was determined.

(2) The thermal treatment was conducted at a thermal treatment shown inTable 3 (150° C.) using a Yankee drier. The thermal treatment time wasset at 45 seconds.

(3) The size of the nonwoven after the thermal treatment was determined.

(4) The area shrinkage percentage was calculated from the above formula.

[Thickness of Nonwoven]

The thickness of the nonwoven after the thermal treatment was determinedusing a thickness meter (manufactured by Daiei Kagaku Seiki SeisakushoCo., Ltd., trade name: THICKNESS GAUGE model CR-60A) under a load of2.94 cN/cm².

[Tensile strength of Nonwoven]

A sample piece of 5 cm in width is held at a grasp interval of 10 cm andextended at a pulling rate of 30±2 cm/min with a constant speedextension tensile tester in accordance with JIS L 1096 6.12.1 A method(strip method). The value of load at break is taken as the tensilestrength. The tensile test was made for each of a lengthwise direction(a machine direction) of the nonwoven and a crosswise direction (a crossdirection). The extension tensile test of the nonwoven produced from thefibers of Sample 10 was made only for one direction.

Experimental Example 1 Evaluation of Fiber Properties and theNonwoven-Processability (Sample 1)

A polyoxymethylene-based polymer was prepared as the first component(the sheath component), of which T_(A) was 156.0° C., MI_(A) was 51, andcontent of CH₂CH₂O as the comonomer was 7.1 mass % as the ethylene oxideequivalent (trade name: V40EX-1 produced by MitsubishiEngineering-Plastics Corporation). A polyoxymethylene-based polymer wasprepared as the second component (the core component), of which T_(B)was 169.0° C., MI_(B) was 28, and content of CH₂CH₂O as the comonomerwas 0.9 mass % as the ethylene oxide equivalent (trade name: A30EX-1produced by Mitsubishi Engineering-Plastics Corporation). These twocomponents were melted and extruded using a sheath-core composite nozzle(an office diameter 0.6 mm: this was the same in the production of thefollowing samples) at a sheath-component spinning temperature of 190° C.and a core-component spinning temperature of 200° C. The composite ratio(volume ratio) of first component/second component was 50/50. The drawratio (spinning draft) was 440 times. As a result, a spun filamenthaving a fineness of 9.9 dtex was obtained.

The spun filament was drawn in hot air of 140° C. with a draw ratio of4.7 times to give a drawn filament having a fineness of about 2 dtex.Next, a fiber treatment agent was applied to the drawn filament andmechanical crimps were formed in the filament with a stuffing box typecrimper. Then, the filament in a relaxed state was subjected to anannealing treatment and a drying treatment at the same time for about 15minutes, in a hot air-through thermal treatment machine wherein atemperature was set at 110° C. The filament was then cut into a fiberlength of 51 mm and a thermoadhesive conjugate fiber in form of a staplefiber was obtained.

[Sample 2]

A thermoadhesive conjugate fiber was produced according to the sameprocedures as those employed in the production of Sample 1, except thatthe setting temperature of the hot air-through thermal treatment (thatis, the temperature for the annealing treatment and the dryingtreatment) was 90° C.

[Sample 3]

A thermoadhesive conjugate fiber was produced according to the sameprocedures as those employed in the production of Sample 1, except thatthe setting temperature of the hot air-through thermal treatment (thatis, the temperature for the annealing treatment and the dryingtreatment) was 60° C.

[Sample 4]

A thermoadhesive conjugate fiber was produced according to the sameprocedures as those employed in the production of Sample 1, except thatthe spun filament was dry-drawn in the hot air of 140° C. at 5.7 timesto obtain a drawn filament having a fineness of about 1.7 dtex and thesetting temperature of the hot air-through thermal treatment (that is,the temperature for the annealing treatment and the drying treatment)was 60° C.

[Sample 5]

A thermoadhesive conjugate fiber was produced according to the sameprocedures as those employed in the production of Sample 1, except thata eccentric sheath-core composite nozzle was used and thecross-sectional structure was made an eccentric sheath-care structurehaving an eccentricity of 40%.

[Sample 6]

A polyoxymethylene-based polymer was prepared as the first component(the sheath component), of which T_(A) was 156.0° C., MI_(A) was 51, andcontent of CH₂CH₂O as the comonomer was 7.1 mass % as the ethylene oxideequivalent (trade name: V40EX-1 produced by MitsubishiEngineering-Plastics Corporation). A polyoxymethylene-based polymer wasprepared as the second component (the core component), of which T_(B)was 169.4° C., MI_(B) was 53, and content of CH₂CH₂O as the comonomerwas 0.9 mass % as the ethylene oxide equivalent (trade name: A40EX-1produced by Mitsubishi Engineering-Plastics Corporation). These twocomponents were melted and extruded using a sheath-core composite nozzleat a sheath-component spinning temperature of 190° C. and acore-component spinning temperature of 200° C. The composite ratio(volume ratio) of first component/second component was 50/50. The drawratio (spinning draft) was 495 times. As a result, a spun filamenthaving a fineness of 8 dtex was obtained.

The spun filament was drawn on a hot plate of 140° C. with a draw ratioof 4.7 times to give a drawn filament having a fineness of about 1.7dtex. Next, a fiber treatment agent was applied to the drawn filamentand mechanical crimps were formed in the filament with a stuffing boxtype crimper. Then, the filament in a relaxed state was subjected to anannealing treatment and a drying treatment at the same time for about 15minutes, in a hot air-through thermal treatment machine wherein atemperature was set at 60° C. The filament was then cut into a fiberlength of 51 mm and a thermoadhesive conjugate fiber in form of a staplefiber was obtained.

[Sample 7]

A thermoadhesive conjugate fiber was produced according to the sameprocedures as those employed in the production of Sample 6, except thatthe setting temperature of the hot air-through thermal treatment (thatis, the temperature for the annealing treatment and the dryingtreatment) was 80° C.

[Sample 8]

A thermoadhesive conjugate fiber was produced according to the sameprocedures as those employed in the production of Sample 6, except thatthe setting temperature of the air-through thermal treatment (that is,the temperature for the annealing treatment and the drying treatment)was 100° C.

[Sample 9: Comparative]

A thermoadhesive conjugate fiber was produced according to the sameprocedures as those employed in the production of Sample 1, except thata polyoxymethylene-based polymer was prepared as the second component(the core component), of which T_(B) was 164° C., MI_(B) was 51, andcontent of CH₂CH₂O as the comonomer was 2.6 mass % as the ethylene oxideequivalent (trade name: F40-73R-1 produced by MitsubishiEngineering-Plastics Corporation) and the setting temperature of the hotair-through thermal treatment (that is, the temperature for theannealing treatment and the drying treatment) was 60° C.

The properties of the staple fibers obtained as Samples 1 to 9 are shownin Tables 1 and 2. In the tables, “−” means that the item was notmeasured, and a box wherein “/” is indicated entirely means that theitem could not be measured since the spinning could not be conducted orthe nonwoven could not be produced.

TABLE 1 Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sheath MI_(A) (g/10min) 51 51 51 51 51 Component Melting Point (T_(A)) (° C.) 156.0 156.0156.0 156.0 156.0 Melting Point (Tf_(A)) (° C.) 153.6 153.6 153.8 154.0154.7 Core MI_(B) (g/10 min) 28 28 28 28 28 Component Melting Point(T_(B)) (° C.) 169.0 169.0 169.0 169.0 169.0 Melting Point (Tf_(B)) (°C.) 167.7 168.2 169.5 170.0 170.1 Eccentric Eccentricity (%) 0 0 0 0 40Form Production Spinning Temperature (° C./° C.) 190/200 190/200 190/200190/200 190/200 Conditions (Sheath/Core) Fineness of Spun (dtex) 9.0 9.09.0 9.0 9.0 Filament Drawing Temperature (° C.) 140 140 140 140 140 DrawRatio (times) 4.7 4.7 4.7 5.7 4.7 Annealing/Drying Temp. (° C.) 110 9060 60 110 Fiber Length (mm) 51 51 51 51 51 Single Fiber Fineness (dtex)2.0 2.0 2.0 1.7 2.0 Properties Strength (cN/dtex) 4.76 4.78 4.81 4.932.85 Elongation (%) 94.1 96.3 103.6 87.6 132.7 Number of Crimps(peaks/25 mm) 116 12.2 16.7 16.5 21.3 Percentage Crimps (%) 7.3 8.8 11.013.8 16.4 Knot Strength (cN) 8.83 8.96 8.94 8.08 4.82 Knot StrengthRetention (%) 92.75 93.72 92.93 96.41 84.56 Single Fiber Initial Tension0.018 mN/dtex (%) 8.11 9.15 10.73 10.01 18.33 Dry Heat ShrinkagePercentage Cardability Δ ∘~Δ ∘ ∘ Δ Nonwoven Process Temperature (° C.)153 153 153 153 153 Nonwoven Area Shrinkage Percentage (%) 7.4 9.9 8.12.7 36.4 Nonwoven Mass Per Unit Area (g/m²) 29.5 30.1 31.6 30.3 —Properties Thickness (mm) 0.61 0.68 0.81 1.01 — Specific Volume (cm³/g)20.5 22.7 25.6 33.3 — Strength MD 65.1 53.0 45.6 56.7 — (N/5 cm) CD 15.515.4 13.5 15.1 —

TABLE 2 Sample 6 Sample 7 Sample 8 Sample 9 Sheath MI_(A) (g/10 min) 5151 51 51 Component Melting Point (T_(A)) (° C.) 156.0 156.0 156.0 156.0Melting Point (Tf_(A)) (° C.) 154.5 154.6 154.6 156.5 Core MI_(B) (g/10min) 53 53 53 51 Component Melting Point (T_(B)) (° C.) 168.3 168.3168.3 164.0 Melting Point (Tf_(B)) (° C.) 171.4 171.5 171.8 162.7Eccentric Eccentricity (%) 0 0 0 0 Form Production Spinning Temperature(° C./° C.) 190/200 190/200 190/200 190/200 Conditions (Sheath/Core)Fineness of Spun Filament (dtex) 8.0 8.0 8.0 9.0 Drawing Temperature (°C.) 140 140 140 140 Draw Ratio (times) 5.0 5.0 5.0 4.7 Annealing/DryingTemp. (° C.) 60 80 100 60 Fiber Length (mm) 51 51 51 51 Single FiberFineness (dtex) 1.68 1.72 1.73 2.0 Properties Strength (cN/dtex) 3.873.69 3.67 2.31 Elongation (%) 36.50 35.90 43.90 134.0 Number of Crimps(peaks/25 mm) 15.20 12.40 18.90 16.5 Percentage Crimps (%) 8.50 6.8010.00 11.3 Knot Strength (cN) 6.31 6.11 6.20 3.32 Knot StrengthRetention (%) 97.05 96.27 97.65 71.86 Single Fiber Initial Tension 0.018mN/dtex (%) 10.20 9.80 8.60 43.41 Dry Heat Shrinkage PercentageCardability ∘ ∘ Δ ∘ Nonwoven Process Temperature (° C.) 155 155 155 155Nonwoven Area Shrinkage Percentage (%) 2.0 1.8 1.8 Nonwoven Mass PerUnit Area (g/m²) 31.4 29.0 30.4 Properties Thickness (mm) 0.72 0.63 0.55Specific Volume (cm³/g) 23.5 21.7 18.1 Strength MD 90.3 75.6 89.9 (N/5cm) CD 20.0 14.8 15.3

The conjugate fibers of Samples 2 to 4, 6 and 7 presented goodcardability and small shrinkage upon the thermal adhesion treatment,which means favorable processability. In contrast, the conjugate fibersof Samples 1, 5 and 8 presented a slightly deteriorated cardability. Itis considered that this is because the annealing temperatures for theconjugate fibers of Samples 1, 5 and 8 were slightly high. Themeasurement of knot strengths and knot strength retentions of Samples 6to 8 showed that knot strength retentions of Samples 6 to 8 were high.

The fiber of Sample 9 could not give a nonwoven because of the shrink ofthe fiber upon the thermal adhesion treatment, although the fiber couldbe produced.

A polyoxymethylene-based polymer was prepared as the first component(the sheath component), of which T_(A) was 155.4° C., MI_(A) was 55, andcontent of CH₂CH₂O as the comonomer was 7.1 mass % as the ethylene oxideequivalent (trade name: V40-EX1 produced by MitsubishiEngineering-Plastics Corporation). A polyoxymethylene-based polymer wasprepared as the second component (the core component), of which T_(B)was 170.4° C., MI_(B) was 55, Mz was 320000, 150° C. ½ crystallizationtime was 25 seconds and content of CH₂CH₂O as the comonomer was 0.9 mass% as the ethylene oxide equivalent (trade name: A40-EX1 produced byMitsubishi Engineering-Plastics Corporation). These two components weremelted and extruded using a sheath-core composite nozzle at asheath-component spinning temperature of 185° C. and a core-componentspinning temperature of 190° C. The composite ratio (volume ratio) offirst component/second component was 50/50. The draw ratio (spinningdraft) was 705 times. As a result, a spun filament having a fineness of4.7 dtex was obtained.

The spun filament was drawn in hot air of 140° C. with a draw ratio of6.5 times to give a drawn filament having a fineness of about 0.8 dtex.Next, a fiber treatment agent was applied to the drawn filament then cutinto a fiber length of 5 mm and a thermoadhesive conjugate fiber in formof a short fiber was obtained.

[Sample 11]

A polyoxymethylene-based polymer was prepared as the first component(the sheath component), of which T_(A) was 155.0° C., MI_(A) was 58, andcontent of CH₂CH₂O as the comonomer was 7.1 mass % as the ethylene oxideequivalent (trade name: V40-EF produced by MitsubishiEngineering-Plastics Corporation). A polyoxymethylene-based polymer wasprepared as the second component (the core component), of which T_(B)was 170.5° C., MI_(B) was 58, Mz was 349000, 150° C. ½ crystallizationtime was 19 seconds and content of CH₂CH₂O as the comonomer was 0.9 mass% as the ethylene oxide equivalent (trade name: A40-EF produced byMitsubishi Engineering-Plastics Corporation). These two components weremelted and extruded using a sheath-core composite nozzle at asheath-component spinning temperature of 185° C. and a core-componentspinning temperature of 190° C. The composite ratio (volume ratio) offirst component/second component was 50/50. The draw ratio (spinningdraft) was 417 times. As a result, a spun filament having a fineness of8.0 dtex was obtained.

The spun filament was drawn in hot air of 140° C. with a draw ratio of5.0 times to give a drawn filament having a fineness of about 1.8 dtex.Next, a fiber treatment agent was applied to the drawn filament andmechanical crimps were formed in the filament with a stuffing box typecrimper. Then, the filament in a relaxed state was subjected to anannealing treatment and a drying treatment at the same time for about 15minutes, in a hot air-through thermal treatment machine wherein atemperature was set at 60° C. The filament was then cut into a fiberlength of 51 mm and a thermoadhesive conjugate fiber in form of a staplefiber was obtained.

[Sample 12]

A thermoadhesive conjugate fiber was produced according to the sameprocedures as those employed in the production of Sample 11, except thatthe spinning temperature of the second component was 200° C. and thedraw ratio of the spun filament was 4.3 times so as to obtain the drawnfilament having a fineness of about 1.9 dtex.

[Sample 13]

A thermoadhesive conjugate fiber was produced according to the sameprocedures as those employed in the production of Sample 11, except thatthe draw ratio (the spinning draft) during the melt extrusion was 572times to obtain the spun filament having a fineness of 5.8 dtex and thefineness of the spun filament after the dry drawing was about 1.3 dtex.

[Sample 14]

A thermoadhesive conjugate fiber was produced according to the sameprocedures as those employed in the production of Sample 11, except thatthe draw ratio (the spinning draft) during the melt extrusion was 572times to obtain the spun filament having a fineness of 5.8 dtex and thedraw ratio of the spun filament was 6.5 times to obtain the drawnfilament having a fineness of about 1.0 dtex.

[Sample 15]

A thermoadhesive conjugate fiber was produced according to the sameprocedures as those employed in the production of Sample 11, except thata polyoxymethylene-based polymer was prepared as the second component(the core component), of which T_(B) was 170.8° C., MI_(B) was 59, Mzwas 357000, 150° C. ½ crystallization time was 10 seconds and content ofCH₂CH₂O as the comonomer was 0.9 mass % as the ethylene oxide equivalent(trade name: A40-EF produced by Mitsubishi Engineering-PlasticsCorporation), the draw ratio (the spinning draft) during the meltextrusion was 572 times to obtain the spun filament having a fineness of5.8 dtex and the draw ratio of the spun filament was 4.3 times to obtainthe drawn filament having a fineness of about 1.3 dtex.

[Sample 16]

A thermoadhesive conjugate fiber was produced according to the sameprocedures as those employed in the production of Sample 11, except thata polyoxymethylene-based polymer was prepared as the second component(the core component), of which T_(B) was 170.8° C., MI_(B) was 59, Mzwas 357000, 150° C. ½ crystallization time was 10 seconds and content ofCH₂CH₂O as the comonomer was 0.9 mass % as the ethylene oxide equivalent(trade name: A40-EF produced by Mitsubishi Engineering-PlasticsCorporation), the draw ratio (the spinning draft) during the meltextrusion was 370 times to obtain the spun filament having a fineness of9.0 dtex and the draw ratio of the spun filament was 4.7 times to obtainthe drawn filament having a fineness of about 2.0 dtex.

[Sample 17]

A polyoxymethylene-based polymer was prepared as the first component(the sheath component), of which T_(A) was 155.0° C., MI_(A) was 61, andcontent of CH₂CH₂O as the comonomer was 7.1 mass % as the ethylene oxideequivalent (trade name: V40-EF produced by MitsubishiEngineering-Plastics Corporation). A polyoxymethylene-based polymer wasprepared as the second component (the core component), of which T_(B)was 171.0° C., MI_(B) was 40, Mz was 400000, 150° C. ½ crystallizationtime was 18 seconds and content of CH₂CH₂O as the comonomer was 0.9 mass% as the ethylene oxide equivalent (trade name: A40-EF-L, produced byMitsubishi Engineering-Plastics Corporation). These two components weremelted and extruded using a sheath-core composite nozzle at asheath-component spinning temperature of 185° C. and a core-componentspinning temperature of 190° C. The composite ratio (volume ratio) offirst component/second component was 50/50. The draw ratio (spinningdraft) was 396 times. As a result, a spun filament having a fineness of8.4 dtex was obtained.

The spun filament was drawn in hot air of 140° C. with a draw ratio of4.7 times to give a drawn filament having a fineness of about 1.8 dtex.Next, a fiber treatment agent was applied to the drawn filament andmechanical crimps were formed in the filament with a stuffing box typecrimper. Then, the filament in a relaxed state was subjected to anannealing treatment and a drying treatment at the same time for about 15minutes, in a hot air-through thermal treatment machine wherein atemperature was set at 60° C. The filament was then cut into a fiberlength of 51 mm and a thermoadhesive conjugate fiber in form of a staplefiber was obtained.

[Sample 18]

A thermoadhesive conjugate fiber was produced according to the sameprocedures as those employed in the production of Sample 17, except thatthe draw ratio (the spinning draft) was 370 times to obtain the spunfilament having a fineness of 9.0 dtex and the resultant fiber having afineness of about 2.0 dtex was obtained.

[Sample 19]

A polyoxymethylene-based polymer was prepared as the first component(the sheath component), of which T_(A) was 155.8° C., MI_(A) was 29, andcontent of CH₂CH₂O as the comonomer was 7.1 mass % as the ethylene oxideequivalent (trade name: V30-EF produced by MitsubishiEngineering-Plastics Corporation). The polyoxymethylene-based polymerwhich was used as the second component in the production of Sample 15was prepared as the second component (the core component). These twocomponents were melted and extruded using a sheath-core composite nozzleat a sheath-component spinning temperature of 185° C. and acore-component spinning temperature of 190° C. The composite ratio(volume ratio) of first component/second component was 50/50. The drawratio (spinning draft) was 370 times. As a result, a spun filamenthaving a fineness of 9.0 dtex was obtained.

The spun filament was drawn in hot air of 140° C. with a draw ratio of4.7 times to give a drawn filament having a fineness of about 2.0 dtex.Next, a fiber treatment agent was applied to the drawn filament andmechanical crimps were formed in the filament with a stuffing box typecrimper. Then, the filament in a relaxed state was subjected to anannealing treatment and a drying treatment at the same time for about 15minutes, in a hot air-through thermal treatment machine wherein atemperature was set at 60° C. The filament was then cut into a fiberlength of 51 mm and a thermoadhesive conjugate fiber in form of a staplefiber was obtained.

[Sample 20]

A thermoadhesive conjugate fiber was produced according to the sameprocedures as those employed in the production of Sample 19, except thatthe draw ratio (the spinning draft) was 417 times to obtain the spunfilament having a fineness of 8.0 dtex and the resultant fiber having afineness of about 1.7 dtex was obtained.

[Sample 21]

A thermoadhesive conjugate fiber having a fineness of 5.8 dtex wasintended to be produced with the draw ratio (the spinning draft) of 572times, but the spinning could not be conducted.

[Sample 22]

The polyoxymethylene-based polymer which was used as the first componentin Sample 19 (trade name: V30-EF produced by MitsubishiEngineering-Plastics Corporation) was prepared as the first component(the sheath component). A polyoxymethylene-based polymer was prepared asthe second component (the core component), of which T_(B) was 161.9° C.,MI_(B) was 31, 150° C. ½ crystallization time was 353 seconds andcontent of CH₂CH₂O as the comonomer was 2.6 mass % as the ethylene oxideequivalent (trade name: F30-EF produced by MitsubishiEngineering-Plastics Corporation). These two components were melted andextruded using a sheath-core composite nozzle at a sheath-componentspinning temperature of 185° C. and a core-component spinningtemperature of 190° C. The composite ratio (volume ratio) of firstcomponent/second component was 50/50. The draw ratio (spinning draft)was 370 times. Under the spinning conditions, a spun filament having afineness of 9.0 dtex was intended to be produced, but the spinning couldnot be conducted.

[Sample 23]

The spun filament having a fineness of 33.0 dtex was intended to beobtained by setting the draw ratio (the spinning ratio) at 100 times,but the spinning could not be conducted.

The properties of the staple fibers obtained as Samples 10 to 23 areshown in Tables 3 to 5. In the tables, “−” means that the item was notmeasured, and a box wherein “/” is indicated entirely means that theitem could not be measured since the spinning could not be conducted orthe nonwoven could not be produced.

TABLE 3 Sample 10 Sample 11 Sample 12 Sample 13 Sheath MI_(A) (g/10 min)55 58 58 58 Component Melting Point (T_(A)) (° C.) 154.4 155.0 155.0155.0 Melting Point (Tf_(A)) (° C.) 155.1 155.5 156.2 156.3 Core MI_(B)(g/10 min) 55 58 58 58 Component Melting Point (T_(B)) (° C.) 170.4170.5 170.5 170.5 Before- Z-Average Molecular Weight Mz 320,000 349,000349,000 349,000 Spinning 150° C. ½ Crystallization Time (seconds) 25 1919 19 Core Wetting Poing (Tf_(B)) (° C.) 171.4 171.7 172.8 171.1Component Z-Average Molecular Weight Mz — — — 289,000 After- 150° C. ½Crystallization Time (seconds) 33.0 20.4 27.0 24.0 Spinning EccentricEccentricity (%) 0 0 0 0 Form Production Spinning Temperature (° C./°C.) 185/190 185/190 185/200 185/190 Conditions (Sheath/Core) Fineness ofSpun Filament (dtex) 4.7 8.0 8.0 5.8 Drawing Temp. (° C.) 140 140 140140 Draw Ratio (times) 6.5 5.0 4.3 5.0 Annealing/Drying Temp. (° C.) 6060 60 60 Fiber Length (mm) 5 51 51 51 Spinnablity ∘ ∘ ∘ ∘ Single FiberFineness (dtex) 0.8 1.8 1.9 1.3 Properties Strength (cN/dtex) 4.4 4.24.0 4.3 Elongation (%) 18 26 22 21 Number of Crimps (peaks/25 mm) 17.116.4 16.7 16.9 Percentage Crimps (%) 12.6 12.4 12.7 12.5 Knot Strength(cN) — — — — Knot Strength Retention (%) — — — — Single Fiber InitialTension 0.018 mN/dtex (%) 6.7 2.4 0 1.8 Dry Heat Shrinkage PercentageCardability — ∘ ∘ ∘ Nonwoven Process Temperature (° C.) 150 140 140 140Nonwoven-Area Shrinkage Percentage (%) 12.3 5.2 0 3.5 Nonwoven Mass PerUnit Area (g/m²) 70 28 28 28 Properties Thickness (mm) 0.20 0.71 0.82060 Specific Volume (cm³/g) 2.85 25.1 29.2 21.6 Strength MD 23 99 98 98(N/5 cm) CD — 20 18 18

TABLE 4 Sample 14 Sample 15 Sample 16 Sample 17 Sample 18 Sheath MI_(A)(g/10 min) 58 58 58 61 61 Component Melting Point (T_(A)) (° C.) 155.0155.0 155.0 155.0 155.0 Melting Point (Tf_(A)) (° C.) 156.7 155.6 155.2155.4 155.3 Core MI_(B) (g/10 min) 58 59 59 40 40 Component MeltingPoint (T_(B)) (° C.) 170.5 170.8 170.8 171.0 171.0 Resin Z-AverageMolecular Weight Mz 349,000 357,000 357,000 400,000 400,000 150° C. ½Crystallization Time (seconds) 19 24 24 18 18 Core Melting Poing(Tf_(B)) (° C.) 172.5 172.2 171.8 171.9 171.7 Component Z-AverageMolecular Weight Mz — — — — — Fiber 150° C. ½ Crystallization Time(seconds) 31.8 13.8 24.0 18.0 18.0 Eccentric Eccentricity (%) 0 0 0 0 0Form Production Spinning Temperature (° C./° C.) 185/200 185/190 165/190185/195 185/195 Conditions (Sheath/Core) Fineness of Spun Filament(dtex) 5.8 5.8 9.0 8.4 9.0 Drawing Temp. (° C.) 140 140 140 140 140 DrawRatio (times) 6.5 4.3 4.7 4.7 4.7 Annealing/Drying Temp. (° C.) 60 60 6060 60 Fiber Length (mm) 51 51 51 51 51 Spinnability ∘ ∘ ∘ Δ ∘ SingleFiber Fineness (dtex) 1.0 1.3 2.0 1.8 2.0 Properties Strength (cN/dtex)4.2 4.1 3.8 3.6 3.9 Elongation (%) 19 19 23 20 21 Number of Crimps(peaks/25 mm) 17.3 16.6 17.2 16.7 17.1 Percentage Crimps (%) 12.3 11.912.2 11.8 12.1 Knot Strength (cN) — — — — — Knot Strength Retention (%)— — — — — Single Fiber Initial Tension 0.018 mN/dtex (%) 0 0 0 0 0 DryHeat Shrinkage Percentage Cardability ∘ ∘ ∘ ∘ ∘ Nonwoven ProcessTemperature (° C.) 156 156 156 156 156 Nonwoven-Area ShrinkagePercentage (%) 0 0 0 0 0 Nonwoven Mass Per Unit Area (g/m³) 30 29 30 2829 Properties Thickness (mm) 0.55 0.61 0.80 0.78 0.79 Specific Volume(cm³/g) 18.3 21.2 26.7 27.9 27.2 Strength MD 96 97 96 99 95 (N/5 cm) CD20 18 19 20 19

TABLE 5 Sample 19 Sample 20 Sample 21 Sample 22 Sample 23 Sheath MI_(A)(g/10 min) 29 29 29 29 29 Component Melting Point (T_(A)) (° C.) 155.8155.8 155.8 155.8 155.8 Melting Point (Tf_(A)) (° C.) 156.1 156.1 156.1156.1 156.1 Core MI_(B) (g/10 min) 59 59 59 31 31 Component MeltingPoint (T_(B)) (° C.) 170.8 170.8 170.8 161.9 161.9 Resin Z-AverageMolecular Weight Mz 357,000 357,000 357,000 — — 150° C. ½Crystallization Time (seconds) 24 24 24 353 353 Core Melting Poing(Tf_(B)) (° C.) 171.4 171.4 171.4 163.1 163.1 Component Z-AverageMolecular Weight Mz — — — — — Fiber 150° C. ½ Crystallization Time(seconds) 26.3 26.3 26.3 366.0 366.0 Eccentric Eccentricity (%) 0 0 0 00 Form Production Spinning Temperature (° C./° C.) 185/190 185/190185/190 185/190 185/190 Conditions (Sheath/Core) Fineness of SpunFilament (dtex) 9.0 8.0 5.8 9.0 33.0 Drawing Temp. (° C.) 140 140 DrawRatio (times) 4.7 4.7 Annealing/Drying Temp. (° C.) 60 60 Fiber Length(mm) 51 51 Spinnablity ∘ ∘ x x x Single Fiber Fineness (dtex) 2.0 1.7Properties Strength (cN/dtex) 3.6 3.7 Elongation (%) 20 19 Number ofCrimps (peaks/25 mm) 16.3 15.5 Percentage Crimps (%) 11.0 9.9 KnotStrength (cN) — — Knot Strength Retention (%) — — Single Fiber InitialTension 0.018 mN/dtex (%) 0 0 Dry Heat Shrinkage Percentage Cardability∘ ∘ Nonwoven Process Temperature (° C.) 156 156 Nonwoven-Area ShrinkagePercentage (%) 0 0 Nonwoven Mass Per Unit Area (g/m²) 29.3 28.8Properties Thickness (mm) 066 0.59 Specific Volume (cm³/g) 22.5 20.5Strength MD 94 98 (N/5 cm) CD 20 18

All of Samples 10 to 16 presented good spinnability and relatively smallsingle fiber dry heat shrinkage percentages. Further, all of Samples 11to 16 presented good cardability and small shrinkage upon the thermaladhesion. As to Sample 10, the wet-laid nonwoven was produced and theshrinkage of this nonwoven was determined. For this reason, the areashrinkage percentage was slightly high, but the percentage was asufficiently practical level. Sample 17 was an example wherein theZ-average molecular weight of 400000 was used as the second component,and the spinnability was slightly deteriorated. Sample 18 wherein thesame second component was used and the spun filament was 9.0 dtex togive the resultant fiber having a fineness of 2.0 dtex, was spun well.

Samples 19 and 20 were spun well, although the before-spinning meltindex was 30 or less. This was because the before-spinning 150° C. ½crystallization time of the second component was 24 seconds. However,when the fineness of the spun filament was made small so that a finerfiber is obtained, the spinning could not be conducted (Sample 21). InSample 22, the spinning could not be conducted when the spun filamentwas set at 9.0 dtex, since the before-spinning melt index of the firstcomponent was 30 or less and the before-spinning 150° C. ½crystallization time of the second component was long. In Sample 23, thespun filament was set at a relatively large fineness to improve thespinnability, using the same resins as those used in Sample 22, but thespinning could not be conducted.

Experimental Example 2 Evaluation of Water Retentivity of Nonwoven

(Sample NW-1)

The water retentivity of a nonwoven of the fibers of the presentinvention was evaluated. Sample 12 produced in Experimental Example 1was used to make a parallel web having a mass per unit area of about 70g/m² and then the web was subjected to a hydroentangling treatment. Thehydroentangling treatment was conducted using a nozzle wherein orificeseach having a 0.1 mm diameter were provided in a line at intervals of0.6 mm. Water streams were applied once to one surface of the web at awater pressure of 3 MPa and the water streams were applied once to theother surface of the web at a water pressure of 3.5 MPa. Then, the webafter the hydroentangling treatment was dried with a hot air-throughthermal treating machine at 160° C. to give a thermally bonded nonwoven.The resultant nonwoven was cut into a size of 10 cm×10 cm and put into awater bath. The nonwoven was impregnated with water sufficiently not tofloat and left in the water bath for 10 minutes. Then, the nonwoven wastaken out and three corners of the four corners are pinched withclothespins and suspended. After suspending the nonwoven for 10 minutes,a mass of the nonwoven was determined and the water retentivity wascalculated from a difference in mass between the nonwoven before andafter being immersed in water. The results are shown in Table 6.

(Sample NW-2; Comparative)

A thermoadhesive conjugate fiber (trade name: NBF(H) produced by DaiwaboPolytec Co., ltd.) wherein the sheath component/the core component was ahigh-density polyethylene/polypropylene, having a fiber length of 51 mmand the fineness of 1.7 dtex, was prepared. The thermally bondednonwoven was produced according to the same procedures as those employedin the production of Sample NW-1, except that the drying temperature wasset at 140° C. Further, the water retentivity of this nonwoven wasdetermined by the same method as that employed in Sample NW-1. Theresults are shown in Table 6.

TABLE 6 Mass after Mass per Mass in Leaving Sample Water Unit AreaThickness Density Dry State in Water for Retention Sample (g/m²) (mm)(g/cm³) (g) 10 min. (g) (%) NW-1 65 0.65 0.100 0.65 4.70 623 NW-2 670.86 0.078 0.67 3.98 494

In general, as the thickness of the nonwoven is larger, the waterretentivity is higher. Although Sample NW-1 is thinner than Sample NW-2,it showed higher water retentivity. This means that the conjugate fiberof the present invention can confer excellent water retentivity to thefiber assembly. The nonwoven showing such water retentivity is suitablefor a wet tissue, a wiper, a mask and so on.

Experimental Example 3 Evaluation of Slippability of Nonwoven

(Sample NW-3)

The slippability of the nonwoven formed from the fibers of the presentinvention was evaluated. Sample 1 produced in Experimental Example 150mass % and rayon fiber (trade name: Corona produced by DAIWABO RAYONCo., Ltd., fineness 1.7 dtex, fiber length 40 mm) 50 mass % were mixedand a parallel web having about a mass per unit area of about 60 g/m²was made using the mixed fibers. The web was subjected to thehydroentangling treatment. The hydroentangling treatment was conductedusing a nozzle wherein orifices each having a 0.1 mm diameter wereprovided in a line at intervals of 0.6 mm. Water streams were applied toone surface of the web once at a water pressure of 3 MPa and the waterstreams were applied to the other surface of the web once at a waterpressure of 3.5 MPa. Then, the web after the hydroentangling treatmentwas dried with a hot air-through thermal treating machine at 160° C. togive a thermally bonded nonwoven.

(Sample NW-4; Comparative)

The thermoadhesive conjugate fiber (trade name: NBF(H) produced byDaiwabo Polytec Co., ltd.) wherein the sheath component/the corecomponent was a high-density polyethylene/polypropylene, having thefiber length of 51 mm and the fineness of 1.7 dtex was prepared. Thethermally bonded nonwoven was produced according to the same proceduresas those employed in the production of Sample NW-3, except that thedrying temperature was set at 140° C.

The slippability of Samples NW-3 and NW-4 were evaluated according tothe following procedures:

(1) The nonwoven was cut into a size of 10 cm×10 cm;

(2) The nonwoven was placed on a glass plate so that the surface towhich the water streams of 3.5 MPa were applied contacted with the glassplate, and an acrylic plate having a thickness of 1 mm was placed on thenonwoven and a weight of 200 g was further placed on the acrylic plate;

(3) The nonwoven and the acrylic plate were pinched with a clip and aspring scale (produced by Sankou Seikohjyo Co. Ltd.) which could measurea load of up to 196 cN was attached to the clip; and

(4) The average load when a laminate of the nonwoven and the acrylicplate was slid 10 cm on the glass plate was read off.

Sample NW-3 showed 44.1 cN as the load described in (4). Sample NW-4showed 53.9 cN as the load described in (4). From these results, it wasfound that the nonwoven produced using the thermoadhesive conjugatefiber of the present invention presented excellent slippablity and thenonwoven was suitable for a wiper or the like used in a dry state.

Experimental Example 4 Production and Evaluation of Personal Wiper

[Sample WP-1]

8-segment splittable conjugate fiber consisting of a combination ofPET/HDPE (trade name: DFS(SH) produced by Daiwabo Polytec Co., ltd.)which has a fineness of 2.2 dtex and a fiber length of 51 mm wasprepared. This splittable conjugate fiber 70 mass % and the conjugatefiber of Sample 1 30 mass % were mixed and then a parallel web having amass per unit area of 50 g/m² was made. The web was subjected to thehydroentangling treatment to entangle the fibers and divide thesplittable conjugate fiber to form ultrafine fibers, using a nozzlewherein orifices each having a 0.1 mm diameter were provided in a lineat intervals of 0.6 mm. Water streams were applied to one surface of theweb once at a water pressure of 3 MPa, and the water streams wereapplied to the other surface of the web once at a water pressure of 3MPa. Next, the web after the hydroentangling treatment was dried with ahot air-through thermal treating machine at 100° C. to give ahydroentangled nonwoven. In this nonwoven, the fibers were not thermallybonded.

[Sample WP-2: Comparative]

A parallel web having a mass per unit area of 50 g/m² was made only fromthe splittable conjugate fibers used in the production of Sample WP-1.This web was subjected to the hydroentangling treatment to divide thesplittable conjugate fiber. The hydroentangling treatment was conductedusing a nozzle wherein orifices each having a 0.1 mm diameter wereprovided in a line at intervals of 0.6 mm. Water streams were applied tothe one surface of the web once at a water pressure of 3 MPa and thewater streams were applied to the other surface of the web once at awater pressure of 3 MPa. Then the web after the hydroentanglingtreatment was dried with a hot air-through thermal treating machine at100° C. to give a hydroentangled nonwoven.

[Sample WP-3: Comparative]

A parallel web having a mass per unit area of 50 g/m² was made only fromcotton (trade name: MS-D produced by MARUSAN INDUSTRY CO., LTD.) andthis web was subjected to the hydroentangling treatment. Thehydroentangling treatment was conducted using a nozzle wherein orificeseach having a 0.1 mm diameter were provided in a line at intervals of0.6 mm. Water streams were applied to one surface of the web once at awater pressure of 2.5 MPa and the water streams were applied to theother surface of the web once at a water pressure of 2.5 MPa. Next, theweb after the hydroentangling treatment was dried using a hotair-through thermal treating machine at 100° C. to give a hydroentanglednonwoven.

The properties of the three samples were evaluated when the samples wereused as the wiper for removing blot from skin of a person. Specifically,the evaluation was conducted according to the following procedures:

(1) Lip rouge was over painted three times on a left palm and left forthree minutes;

(2) The sample was cut into a size of 5 cm×10 cm

(the lengthwise direction (MD)×crosswise direction (CD));

(3) The lip rouge was wiped off by rubbing the left palm three times bymeans of the sample applying a little pressure. The sample and the leftpalm were observed and the wiping-ability was evaluated according to thefollowing standards;

1: Much blot remained;

2: Blot left on the left palm was noticeable;

3: Much blot was transferred to the surface of the sample, but a littleblot remained (slightly noticeable);

4: Much blot was transferred to the surface of the sample and a tinyamount of blot remained (not noticeable);

5: Much blot was transferred into the sample and a tiny amount of blotremained (not noticeable).

Further, the similar wiping-ability was evaluated by over-paintingeyebrow on the left palm.

Furthermore, the feel of each sample was evaluated according to thefollowing standards:

1: Hard and rough;

2: Hard and slightly rough;

3: Slightly hard and slightly rough;

4: Soft and slightly rough;

5: Soft and not rough.

Furthermore, the rigidity of each sample was determined using ahandleometer (model type HOM-200, manufactured by Daiei Kagaku SeikiSeisakusho Co., Ltd.). More specifically, a test piece of 20 cm×17.5 cm(the lengthwise direction (MD)×the crosswise direction (CD)) was set ona slit of a 10 mm width perpendicular to the slit and the test piece waspushed by 8 mm at a position shifted by 6.7 cm from the side of the testpiece (at a position of one third of the testing width) using a blade ofa penetrator and a resistance value was measured as the stiffness. Theresistance values during the push were measured at two different pointsfor each of the lengthwise direction and the crosswise direction (CD)respectively of one sample, and the sum of the measured four values wasevaluated as the rigidity.

The evaluation results are shown in Table 7.

TABLE 7 Mass per Unit Area Thickness Rigidity Wiping-Ability Sample(g/m²) (mm) Feeling (g) Rouge Eyebrow WP-1 54 0.72 5 18.9 5 5 WP-2 540.76 5 22.1 5 5 WP-3 48 0.65 3 26.1 3 3

Sample WP-3 made of cotton that is widely used in a sheet for removingcosmetics were inferior in feeling and wiping-ability compared to theother samples and had a large rigidity and hard and rough feeling. Incontrast, Sample WP-2 which contains ultrafine fibers formed by divisionof the splittable conjugate fiber had good feeling and wiping-ability,as already known to those skilled in the art. Sample WP-1 containing theconjugate fiber of the present invention presented the feeling and thewiping-ability equivalent to those of Sample WP-2 although the contentof the splittable fibers (that is, the ultrafine fibers) in Sample WP-1was smaller than that in Sample WP-2. Further, the rigidity of SampleWP-1 is the smallest among the three samples. Therefore, Sample WP-1 wasvery soft. Furthermore, as shown in Experimental Example 3, since theconjugate fiber of the present invention improved the slippability ofthe nonwoven, Sample WP-1 was an excellent wiper which enabled the blotto be removed by lightly wiping the skin therewith. These mean that theconjugate fiber of the present invention is suitable for constitutingthe wiper.

Experimental Example 5 Evaluation of Impersonal Wiper

[Sample WP-4]

8-segment splittable conjugate fiber consisting of a combination ofPET/HDPE (trade name: DFS(SH) produced by Daiwabo Polytec Co., ltd.)having a fineness of 2.2 dtex and a fiber length of 51 mm was prepared.This splittable conjugate fiber 70 mass % and the conjugate fiber ofSample 1 30 mass % were mixed and then two parallel webs each of whichhad a mass per unit area of 27 g/m² were made. A tissue (produced byHavix Corporation) having a mass per unit area of 17 g/m² which was madefrom wood pulp was sandwiched with these two webs to give a a laminatedweb of three-layer structure.

This laminated web was subjected to the hydroentangling treatment toentangle the fibers and divide the splittable conjugate fiber to formultrafine fibers. The hydroentangling treatment was conducted using anozzle wherein orifices each having a 0.1 mm diameter are provided in aline at intervals of 0.6 mm. Water streams were applied to one surfaceof the web once at a water pressure of 3 MPa and the water streams wereapplied to the other surface of the web once at a water pressure of 3.5MPa. Then the web after the hydroentangling treatment was dried with ahot air-through thermal treating machine at 100° C. to give ahydroentangled nonwoven. In this nonwoven, the fibers were not thermallybonded.

[Sample WP-5]

16-segment splittable conjugate fiber consisting of a combination ofPET/PP (trade name: DF-1 produced by Daiwabo Polytec Co., ltd.) having afineness of 3.3 dtex and a fiber length of 51 mm was prepared. Ahydroentangled nonwoven of laminated structure was produced according tothe same procedures as those employed in the production of Sample WP-4,except that only this splittable conjugate fiber was used.

[Sample WP-6]

A hydroentangled nonwoven of laminate structure was produced accordingto the same procedures as those employed in the production of SampleWP-4, except that only the splittable fiber used in the production ofSample WP-4 was used.

The performance of each of these samples was evaluated when using eachsample as a wiper to remove dirt adhered to a surface of a impersonalobject. Specifically, the evaluation was conducted according to thefollowing procedures:

The nonwoven was cut into a size of 20 cm×60 cm (the crosswise direction(CD)×the lengthwise direction (MD)) and folded in eightmo. Then, thesample was impregnated with a 50% aqueous solution wherein “FukupikaSpray Wax” (trade name) (produced by SOFT 99 Corporation) was dilutedwith water. The sample was impregnated with the aqueous solution of 250mass % relative to the mass of the sample. The wetted sample was movedback and forth ten times on a portion of painted surface of a car bodyto remove the dirt. The operation for removing the dirt was repeatedtwice. Further, the sample was moved back and forth ten times on anotherportion of the painted surface of the car body, while lightness ofwiping, how liquid is released, kink, fuzz, liquid remain, andwiping-ability were evaluated according to the following standards:

[Lightness]

1 Heavy and difficult to use for wiping operation;

2 Little heavy, but no problem to use for wiping operation;

3 Light, but little resistance feeling;

4 Light and easy to use for wiping operation.

[How Liquid is Discharged]

1 Liquid is discharged at one time, and can be used for wiping only asmall area;

2 Liquid is discharged slightly more, and can be used for wiping anot-large area;

3 Liquid is discharged adequately, but can be used for wiping aslightly-reduced area;

4 Liquid is discharged adequately, and can be used for wiping a largearea broad.

[Kink]

1 Kink starts to be made just after starting wiping;

2 Kink does not occur when starting wiping, but kink occurs slightlyafter a short time;

3 kink does not occur when starting wiping, but very slight kink occursafter a short time;

4 Very slight kink occurs when liquid in the sample starts to evaporate.

[Fuzz]

1 Fuzz generates;

2 A little fuzz generates during the use of the sample;

3 Fluff generates on the sample surface, but fuzz does not generateduring the use of the sample;

4 A little fluff generates.

[Liquid Remain]

1 Water droplets on the object being wiped after wiping are large anddifficult to dry;

2 Water droplets on the object being wiped after wiping are slightlylarge and require a slightly long time for drying;

3 Water droplets on the object being wiped after wiping are small anddry in a little while;

4 Water droplets on the object being wiped after wiping are minute anddry in a little while.

[Wiping-Ability]

1 Dirt cannot be wiped off cleanly;

2 Dirt can be wiped off cleanly after moving the sample back and forthfive or six times;

3 Dirt can be wiped off cleanly after moving the sample back and forthtwo or three times;

4 Dirt can be wiped off cleanly after moving one or two times.

The results of evaluation are shown in Table 8.

TABLE 8 Lightness How Liquid (Wiping Is Liquid Wiping- SampleComfortableness) Discharged Kink Lint Remain Ability Total WP-4 3 4 3 34 3 20 WP-5 4 2 2 2 2 2 14 WP-6 4 4 2 3 4 3 20

Although Sample WP-4 had a construction wherein the upper and the lowerlayers contained the conjugate fibers of the present invention whichwere not the splittable fibers, it presented more excellentwiping-ability than Sample WP-5 wherein the upper and the lower layersconsist only of the splittable fibers. Further, Sample WP-4 showedbetter results for all items except for “lightness” than Sample WP-5.Sample WP-6 was formed only from the splittable conjugate fiber whichconstituted Sample 4 and had more ultrafine fibers than Sample WP-4.Nevertheless, Sample WP-4 presented the same properties as those ofSample WP-6. These mean that the conjugate fiber of the presentinvention is suitable for constituting the wiper.

Experimental Example 6 Evaluation of Compression Recoverability ofNonwoven

[Sample MA-1: Comparative]

A high-elastic PET fiber (trade name: elk produced by TEIJIN FIBERSLIMITED, fineness 6.6 dtex, fiber length 64 mm) 30 mass % and a hollowPET fiber (trade name: H18F produced by Unitika Ltd., fineness 6.7 dtex,fiber length 51 mm) 50 mass % and a latently crimpable PET fiber (tradename: C81, produced by Unitika Ltd., fineness 2.8 dtex, fiber length 51mm) 20 mass % were mixed, and a parallel web was made using this mixedfibers and then the webs were laminated using a cross layer to give alaminated web having a mass per unit area of 800 g/m². The laminated webwas subjected to a thermal treatment for seven minutes with an oven at200° C. to give a bulky sponge-like nonwoven having a thickness of 28mm.

[Sample MA-2]

A parallel web was made from the sheath-core conjugate fiber of Sample 3produced in Experimental Example 1. Then, the webs were laminated with across layer to give a laminated web having a mass per unit area of 800g/m². The laminated web was subjected to a thermal treatment for sevenminutes at 156° C. to give a bulky sponge-like nonwoven having athickness of 25 mm.

Each of the samples was cut into a size of 10 cm×10 cm and a weight of5.6 kg was placed thereon and left for 24 hours. Then, the weight wasremoved and the thickness of the nonwoven was determined over time toevaluate the bulk recoverability. The results of the evaluation areshown in Table 9.

TABLE 9 After Removing Weight 0 5 10 20 60 150 360 24 Sample InitialWeighted min. min min. min. min min min. hours MA-1 Thickness 28.0  8.024.0 25.0 25.5 26.0 26.5 26.5 27.0 27.0 (mm) Recovery — — 85.7 89.3 91.192.9 94.6 94.6 24.0 96.4 Rate (%) MA-2 Thickness 25.0 15.0 19.0 20.021.0 22.0 23.0 23.5 24.0 25.0 (mm) Recovery — — 76.0 80.0 84.0 88.0 92.094.0 96.0 100.0 Rate (%)

Sample MA-1 made for comparison containing the high elastic fiber andthe latently crimpable fiber was bulky enough to be used as, forexample, a bed mat, and had high compression recoverability,particularly high initial bulk recoverability. On the other hand, thethermoadhesive conjugate fiber of the present invention showed a bulkrecovery percentage of 100% 24 hours after removing weight and presentedhigh bulk recoverability although it does not have latently crimpabilityand elasticity. The nonwoven presenting such bulk recoverability issuitable for using as a cushion material, a brassier pad and so on.

Experimental Example 7 Evaluation of Crease Resistance and Rigidity ofNonwoven

[Sample WR-1: Comparative]

A parallel carded web having a mass per unit area of 28.7 g/m² was madefrom a concentric sheath-core conjugate fiber wherein sheath/core wasHDPE/PET and sheath:core (mass ratio) was 1:1 (trade name: NBF(SH)produced by Daiwabo Polytec Co., ltd., fineness 2.2 dtex, fiber length51 mm). This web was subjected to a thermal treatment using a hotair-through thermal treating machine at 140° C. for 12 seconds to give athermally bonded nonwoven with a thickness of 1.45 mm.

[Sample WR-2]

A parallel carded web having a mass per unit area of 27.4 g/m² was madefrom the sheath-core conjugate fiber of Sample 3 produced inExperimental Example 1. This web was subjected to a thermal treatment at156° C. for 12 seconds to give a thermally bonded nonwoven having athickness of 0.85 mm.

As to each of the two samples, the crease resistance percentage (wiremethod) was determined according to JIS L 1085, and the rigidity wasdetermined according to JIS L 1096 (45° cantilever method). The resultsare shown in Table 10.

TABLE 10 Mass per Crease Unit Area Thickness Angle α Resistance RigiditySample (g/m²) (mm) (°) Percentage (%) (mm) WR-1 28.7 1.45 145 80.6 120WR-2 27.4 0.85 178 99.0 160

Sample WR-1 made from a general thermoadhesive conjugate fiber was softand had a tendency of creasing. In contrast, Sample WR-2 made from thethermoadhesive conjugate fiber of the present invention had a higherrigidity than Sample WR-1. Further, this sample presented high creaseresistance such that, when the sample was released from folded state,the sample opened instantly and returned to an original shape withoutcrease. The nonwoven having such high crease resistance is suitable fora constituent for a hygiene product such as a menstrual sanitary productand a paper diaper (for example, a sheet for retaining a shape of thehygiene product) and an interfacing.

Experimental Example 8 Production of Molded Article

A parallel carded web was made from the fiber of Sample 12 produced inExperimental Example 1 and the webs were laminated using a cross layerto give a laminated web having a mass per unit area of 200 g/m². Then,the laminated web was cut into a size of 20 cm×20 cm.

Two hemisphere tea strainers made of metal mesh were prepared, one beingof a dimension of 060 mm×a depth of 60 mm, and the other being of adimension of 050 mm×a depth of 55 mm. The two tea strainers were stackedwith the laminated web interposed between the strainers. The websandwiched with the two tea strainers was subjected to a thermaltreatment at 161° C. for 15 minutes with a batch-type hot air-throughthermal treating machine. After the thermal treatment, the tea strainerswere removed, and thereby a cup-shaped molded article having a wallthickness of 5 mm and a round bottom was obtained. Such a molded articleis suitable for being used as, for example, a filter.

INDUSTRIAL APPLICABILITY

The thermoadhesive conjugate fiber of the present invention is onewherein the respective components are formed from polyoxymethylene-basedpolymers, whereby a fiber assembly (particularly a nonwoven) wherein thefibers are bonded only with a polyoxymethylene-based polymer can beproduced. Further, the thermoadhesive conjugate fiber of the presentinvention confers, to the fiber assembly, high water retentivity, highslippability, crease resistance, and bulk recoverability and favorablewiping-ability. Therefore, the thermoadhesive conjugate fiber of thepresent invention is useful for producing the fiber assembly applicableto various uses for which heat resistance and chemical resistance aredesired.

1. A thermoadhesive conjugate fiber comprising a first component as athermoadhesive component which comprises a polyoxymethylene-basedpolymer A and a second component which comprises apolyoxymethylene-based polymer B, wherein the first component is exposedwith an exposed length of not less than 20% relative to a peripherallength of the fiber, which fiber satisfies: 30<MI_(A) wherein MI_(A) isa before-spinning melt index (g/10 min) of the polyoxymethylene-basedpolymer A, which is determined according to JIS K 7210 (conditions: 190°C., load: 21.18N (2.16 kg)), a before-spinning 150° C. ½ crystallizationtime of the polyoxymethylene-based polymer B is not less than 10 secondsand less than 30 seconds, and Tf_(B)>Tf_(A)+10 wherein Tf_(A) and Tf_(B)are after-spinning fusion peak temperatures of thepolyoxymethylene-based polymers A and B respectively, which aredetermined according to JIS K
 7121. 2. (canceled)
 3. The thermoadhesiveconjugate fiber according to claim 1, wherein an after-spinning 150° C.½ crystallization time of the polyoxymethylene-based polymer B is from10 seconds to 100 seconds.
 4. A thermoadhesive conjugate fibercomprising a first component as a thermoadhesive component whichcomprises a polyoxymethylene-based polymer A and a second componentwhich comprises a polyoxymethylene-based polymer B, wherein: the firstcomponent is exposed with an exposed length of not less than 20%relative to a peripheral length of the fiber, a before-spinning 150° C.½ crystallization time of the polyoxymethylene-based polymer B is notless than 10 seconds and less than 30 seconds, and Tf_(B)>Tf_(A)+10wherein Tf_(A) and Tf_(B) are after-spinning fusion peak temperatures ofthe polyoxymethylene-based polymers A and B respectively, which aredetermined according to JIS K
 7121. 5. A thermoadhesive conjugate fibercomprising a first component as a thermoadhesive component whichcomprises a polyoxymethylene-based polymer A and a second componentwhich comprises a polyoxymethylene-based polymer B, wherein: the firstcomponent is exposed with an exposed length of not less than 20%relative to a peripheral length of the fiber, an after-spinning 150° C.½ crystallization time of the polyoxymethylene-based polymer B is from10 seconds to 100 seconds, and Tf_(B)>Tf_(A)+10 wherein Tf_(A) andTf_(B) are after-spinning fusion peak temperatures of thepolyoxymethylene-based polymers A and B respectively, which aredetermined according to JIS K
 7121. 6. The thermoadhesive conjugatefiber according to claim 4, wherein a before-spinning Z-averagemolecular weight of the polyoxymethylene-based polymer B is 500,000 orless.
 7. The thermoadhesive conjugate fiber according to claim 5,wherein an after-spinning Z-average molecular weight of the conjugatefiber is 350,000 or less.
 8. The thermoadhesive conjugate fiberaccording to claim 4, which is a sheath-core conjugate fiber consistingof the first component and the second component, the first componentbeing a sheath component and the second component being a corecomponent.
 9. The thermoadhesive conjugate fiber according to claim 8,which has an eccentric sheath-core cross section in which a centerposition of the second component is shifted from the center position ofthe fiber.
 10. A method for producing a thermoadhesive conjugate fiberwhich comprises: providing two kinds of polyoxymethylene-based polymersA and B which satisfy: 30<MI_(A) wherein MI_(A) is a before-spinningmelt index (g/10 min) of the polyoxymethylene-based polymer A, which isdetermined according to JIS K 7210 (conditions: 190° C., load: 21.18N(2.16 kg)), a before-spinning 150° C. ½ crystallization time of thepolyoxymethylene-based polymer B is not less than 10 seconds and lessthan 30 seconds, and T_(B)>T_(A)+10 wherein T_(A) and T_(B) arebefore-spinning fusion peak temperatures of the polyoxymethylene-basedpolymers A and B respectively, which are determined according to JIS K7121, compositely spinning a first component comprising thepolyoxymethylene-based polymer A and a second component comprising thepolyoxymethylene-based polymer B such that the first component isexposed with an exposed length of not less than 20% relative to aperipheral length of the fiber, subjecting the spun fiber to a drawingtreatment, and subjecting the drawn fiber to an annealing treatment at atemperature of from 60° C. to 110° C.
 11. (canceled)
 12. A method forproducing a thermoadhesive conjugate fiber, which comprises: providingtwo kinds of polyoxymethylene-based polymers A and B, the polymer Bhaving a before-spinning 150° C. ½ crystallization time of not less than10 seconds and less than 30 seconds, and the polymers satisfyingT_(B)>T_(A)+10 wherein T_(A) and T_(B) are before-spinning fusion peaktemperatures of the polyoxymethylene-based polymers A and B respectivelywhich temperatures are determined according to JIS K 7121, compositelyspinning a first component comprising the polyoxymethylene-based polymerA and a second component comprising the polyoxymethylene-based polymer Bsuch that the first component is exposed with an exposed length of notless than 20% relative to a peripheral length of the fiber, subjectingthe spun fiber to a drawing treatment, and subjecting the drawn fiber toan annealing treatment at a temperature of from 60° C. to 110° C. 13.The method for producing a thermoadhesive conjugate fiber according toclaim 12, wherein the annealing is conducted at a temperature of from60° C. to 90° C.
 14. The method for producing a thermoadhesive conjugatefiber according to claim 12, wherein spinning is conducted at a draftratio of from 100 times to 1000 times and the drawing is conducted at adraw ratio of from 4 times to 10 times.
 15. A fiber assembly comprisingthe thermoadhesive conjugate fiber according to claim 4 in an amount of10 mass % or more.
 16. The fiber assembly according to claim 15, whereinthe fibers are thermally bonded to each other.
 17. The fiber assemblyaccording to claim 15, which is a nonwoven.
 18. A wiper which comprisesthe nonwoven according to claim
 17. 19. The fiber assembly according toclaim 15, which is a molded article.